Nauvoo, Illinois, September 6, 1842
More on baptizing dead people
1 As I stated to you in my letter before I left my place, that I would write to you from time to time and give you information in relation to many subjects,I now resume the subject of the baptism for the dead, as that subject seems to occupy my mind, and press itself upon my feelings the strongest, since I have been pursued by my enemies.
I [Joseph Smith] told you in my letter before leaving that I'd write you from time to time.
So now I'll tell you some more about baptizing dead people.
2 I wrote a few words of revelation to you concerning a recorder. I have had a few additional views in relation to this matter, which I now certify. That is, it was declared in my former letter that there should be a recorder, who should be eye-witness, and also to hear with his ears, that he might make a record of a truth before the Lord.
These baptisms must be witnessed and recorded.
3 Now, in relation to this matter, it would be very difficult for one recorder to be present at all times, and to do all the business. To obviate this difficulty, there can be a recorder appointed in each ward of the city, who is well qualified for taking accurate minutes; and let him be very particular and precise in taking the whole proceedings, certifying in his record that he saw with his eyes, and heard with his ears, giving the date, and names, and so forth, and the history of the whole transaction; naming also some three individuals that are present, if there be any present, who can at any time when called upon certify to the same, that in the mouth of two or three witnesses every word may be established.
4 Then, let there be a general recorder, to whom these other records can be handed, being attended with certificates over their own signatures, certifying that the record they have made is true. Then the general church recorder can enter the record on the general church book, with the certificates and all the attending witnesses, with his own statement that he verily believes the above statement and records to be true, from his knowledge of the general character and appointment of those men by the church. And when this is done on the general church book, the record shall be just as holy, and shall answer the ordinance just the same as if he had seen with his eyes and heard with his ears, and made a record of the same on the general church book.
5 You may think this order of things to be very particular; but let me tell you that it is only to answer the will of God, by conforming to the ordinance and preparation that the Lord ordained and prepared before the foundation of the world, for the salvation of the dead who should die without a knowledge of the gospel.
Sometime before the world began, the Lord decided to save people who didn't hear the gospel while they were alive by baptizing them after they were dead.
6 And further, I want you to remember that John the Revelator was contemplating this very subject in relation to the dead, when he declared, as you will find recorded in Revelation 20:12—And I saw the dead, small and great, stand before God; and the books were opened; and another book was opened, which is the book of life; and the dead were judged out of those things which were written in the books, according to their works.
7You will discover in this quotation that the books were opened; and another book was opened, which was the book of life; but the dead were judged out of those things which were written in the books, according to their works; consequently, the books spoken of must be the books which contained the record of their works, and refer to the records which are kept on the earth. And the book which was the book of life is the record which is kept in heaven; the principle agreeing precisely with the doctrine which is commanded you in the revelation contained in the letter which I wrote to you previous to my leaving my place—that in all your recordings it may be recorded in heaven.
8 Now, the nature of this ordinance consists in the power of the priesthood, by the revelation of Jesus Christ, wherein it is granted that whatsoever you bind on earth shall be bound in heaven, and whatsoever you loose on earth shall be loosed in heaven. Or, in other words, taking a different view of the translation, whatsoever you record on earth shall be recorded in heaven, and whatsoever you do not record on earth shall not be recorded in heaven; for out of the books shall your dead be judged, according to their own works, whether they themselves have attended to the ordinances in their own propria persona, or by the means of their own agents, according to the ordinance which God has prepared for their salvation from before the foundation of the world, according to the records which they have kept concerning their dead.
When Jesus said,
Whatever you bind on earth shall be bound int heaven, etc.
what he really meant was (if translated properly),
Whatever you record on earth shall be recorded in heaven, etc.
9 It may seem to some to be a very bold doctrine that we talk of—a power which records or binds on earth and binds in heaven. Nevertheless, in all ages of the world, whenever the Lord has given a dispensation of the priesthood to any man by actual revelation, or any set of men, this power has always been given. Hence, whatsoever those men did in authority, in the name of the Lord, and did it truly and faithfully, and kept a proper and faithful record of the same, it became a law on earth and in heaven, and could not be annulled, according to the decrees of the great Jehovah. This is a faithful saying. Who can hear it?
This is a faithful saying. Who can hear it?
10 And again, for the precedent, Matthew 16:18, 19: And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven; and whatsoever thou shalt loose on earth shall be loosed in heaven.
11 Now the great and grand secret of the whole matter, and the summum bonum of the whole subject that is lying before us, consists in obtaining the powers of the Holy Priesthood. For him to whom these keys are given there is no difficulty in obtaining a knowledge of facts in relation to the salvation of the children of men, both as well for the dead as for the living.
12 Herein is glory and honor, and immortality and eternal life—The ordinance of baptism by water, to be immersed therein in order to answer to the likeness of the dead, that one principle might accord with the other; to be immersed in the water and come forth out of the water is in the likeness of the resurrection of the dead in coming forth out of their graves; hence, this ordinance was instituted to form a relationship with the ordinance of baptism for the dead, being in likeness of the dead.
13 Consequently, the baptismal font was instituted as a similitude of the grave, and was commanded to be in a place underneath where the living are wont to assemble, to show forth the living and the dead, and that all things may have their likeness, and that they may accord one with another—that which is earthly conforming to that which is heavenly, as Paul hath declared, 1 Corinthians 15:46, 47, and 48:
The baptismal font was made to look like a grave, as Paul declared in 1 Corinthians 15:46-47. 
14 Howbeit that was not first which is spiritual, but that which is natural; and afterward that which is spiritual. The first man is of the earth, earthy; the second man is the Lord from heaven. As is the earthy, such are they also that are earthy; and as is the heavenly, such are they also that are heavenly. And as are the records on the earth in relation to your dead, which are truly made out, so also are the records in heaven. This, therefore, is the sealing and binding power, and, in one sense of the word, the keys of the kingdom, which consist in the key of knowledge.
15 And now, my dearly beloved brethren and sisters, let me assure you that these are principles in relation to the dead and the living that cannot be lightly passed over, as pertaining to our salvation. For their salvation is necessary and essential to our salvation, as Paul says concerning the fathers—that they without us cannot be made perfect—neither can we without our dead be made perfect.
If you are to be saved, dead people must also be saved.
As Paul said, 
Dead people can't be made perfect without us,
and we can't be made perfect without dead people.
16 And now, in relation to the baptism for the dead, I will give you another quotation of Paul, 1 Corinthians 15:29: Else what shall they do which are baptized for the dead, if the dead rise not at all? Why are they then baptized for the dead?
Paul said this in 1 Corinthians 15:29 about baptizing dead people: 
Else what shall they do which are baptized for the dead, if the dead rise not at all?
Why are they then baptized for the dead?
17 And again, in connection with this quotation I will give you a quotation from one of the prophets, who had his eye fixed on the restoration of the priesthood, the glories to be revealed in the last days, and in an especial manner this most glorious of all subjects belonging to the everlasting gospel, namely, the baptism for the dead; for Malachi says, last chapter, verses 5th and 6th: Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
Malachi 4:5-6 says:
Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
18 I might have rendered a plainer translation to this, but it is sufficiently plain to suit my purpose as it stands. It is sufficient to know, in this case, that the earth will be smitten with a curse unless there is a welding link of some kind or other between the fathers and the children,upon some subject or other—and behold what is that subject? It is the baptism for the dead. For we without them cannot be made perfect; neither can they without us be made perfect. Neither can they nor we be made perfect without those who have died in the gospel also; for it is necessary in the ushering in of the dispensation of the fulness of times, which dispensation is now beginning to usher in, that a whole and complete and perfect union, and welding together of dispensations, and keys, and powers, and glories should take place, and be revealed from the days of Adam even to the present time. And not only this, but those things which never have been revealed from the foundation of the world, but have been kept hid from the wise and prudent, shall be revealed unto babes and sucklings in this, the dispensation of the fulness of times.
I could make a better translation of this verse, but you get the idea.
It's enough to know that God plans to smite the earth with a curse - unless there's a link of some kind between fathers and children.
And that something is the baptism of dead people.
Because we can't be made perfect without dead people, and dead people can't be made perfect without us.
Also the end times won't come unless we baptize dead people.
19 Now,what do we hear in the gospel which we have received? A voice of gladness! A voice of mercy from heaven; and a voice of truth out of the earth; glad tidings for the dead; a voice of gladness for the living and the dead; glad tidings of great joy. How beautiful upon the mountains are the feet of those that bring glad tidings of good things, and that say unto Zion: Behold, thy God reigneth! As the dews of Carmel, so shall the knowledge of God descend upon them!
What do we hear from the gospel?
Glad tidings for dead people.
How beautiful on the mountains are the feet of those who bring glad tidings. 
20 And again, what do we hear? Glad tidings from Cumorah! Moroni, an angel from heaven, declaring the fulfilment of the prophets—the book to be revealed. A voice of the Lord in the wilderness of Fayette, Seneca county, declaring the three witnesses to bear record of the book! The voice of Michael on the banks of the Susquehanna, detecting the devil when he appeared as an angel of light! The voice of Peter, James, and John in the wilderness between Harmony, Susquehanna county, and Colesville, Broome county, on the Susquehanna river, declaring themselves as possessing the keys of the kingdom, and of the dispensation of the fulness of times!
So what do we hear?
Glad tidings from Cumorah!
The angel Moroni revealing a new book to be published.
The voice of the Lord in Fayette, Seneca County with three men who saw the book.
Michael on the banks of the Susquehanna with a devil detector.
Peter, James and John somewhere between Harmony, Susquehanna county, and Colesville, Broome county, on the Susquehanna River with the keys to the kingdom.
21 And again, the voice of God in the chamber of old Father Whitmer, in Fayette, Seneca county, and at sundry times, and in divers places through all the travels and tribulations of this Church of Jesus Christ of Latter-day Saints! And the voice of Michael, the archangel; the voice of Gabriel, and of Raphael, and of divers angels, from Michael or Adam down to the present time, all declaring their dispensation, their rights, their keys, their honors, their majesty and glory, and the power of their priesthood; giving line upon line, precept upon precept; here a little, and there a little; giving us consolation by holding forth that which is to come, confirming our hope!
And again, the voice of God in old Father Whitmer's room in Fayette, Seneca County.
The voices of Michael, Gabriel, and Rphael the Archangels and other angels.
22 Brethren, shall we not go on in so great a cause? Go forward and not backward. Courage, brethren; and on, on to the victory! Let your hearts rejoice, and be exceedingly glad. Let the earth break forth into singing. Let the dead speak forth anthems of eternal praise to the King Immanuel, who hath ordained, before the world was, that which would enable us to redeem them out of their prison; for the prisoners shall go free.
Go forward, not backward.
On to victory!
Let the earth start singing and dead people start talking.
23 Let the mountains shout for joy, and all ye valleys cry aloud; and all ye seas and dry lands tell the wonders of your Eternal King! And ye rivers, and brooks, and rills, flow down with gladness. Let the woods and all the trees of the field praise the Lord; and ye solid rocks weep for joy! And let the sun, moon, and the morning stars sing together, and let all the sons of God shout for joy! And let the eternal creations declare his name forever and ever! And again I say, how glorious is the voice we hear from heaven, proclaiming in our ears, glory, and salvation, and honor, and immortality, and eternal life; kingdoms, principalities, and powers!
Shout for joy, you mountains, valleys, seas, dry lands, rivers, woods, and trees.
And you rocks, weep for joy.
Sun, moon, and start - start singing.
24 Behold, the great day of the Lord is at hand; and who can abide the day of his coming, and who can stand when he appeareth? For he is like a refiner’s fire, and like fuller’s soap; and he shall sit as a refiner and purifier of silver, and he shall purify the sons of Levi, and purge them as gold and silver, that they may offer unto the Lord an offering in righteousness. Let us, therefore, as a church and a people, and as Latter-day Saints, offer unto the Lord an offering in righteousness; and let us present in his holy temple, when it is finished, a book containing the records of our dead, which shall be worthy of all acceptation.
The Lord's great day is nearly here.
He's like fuller's soap.
Let's finish this temple an put the records of the dead people that we've baptized in it.
25 Brethren, I have many things to say to you on the subject; but shall now close for the present, and continue the subject another time. I am, as ever, your humble servant and never deviating friend, Joseph Smith.
I have a lot more to say, but I'll save it for later.
I'm your humble servant, Joseph Smith.
- As Paul hath declared, 1 Corinthians 15:46-47 (v.13)
The baptismal font was made to look like a grave, as is perfectly obvious when you read the actual verses.
Howbeit that was not first which is spiritual, but that which is natural; and afterward that which is spiritual.
The first man is of the earth, earthy; the second man is the Lord from heaven." >1 Corinthians 15:46-47
- As Paul says concerning the fathers - that they without us cannot be made perfect - neither can we without our dead be made perfect.(v.15)
The text doesn't say where Paul supposedly said this, but the LDS church's footnote for this is Hebrews 11:40, which says,
God having provided some better thing for us, that they without us should not be made perfect.
But the author of Hebrews doesn't claim to be Paul (and wasn't Paul), and it isn't clear who the "them" is that need us to be made perfect.
- 1 Corinthians 15:29 (v.16)
This is the verse that is most often used to justify baptizing dead people. And it does sound like Paul was in favor of the practice. (But then, you can find support for just about any belief in the Bible - no matter how crazy.)
- Beautiful feet (v.19)
Joseph Smith had a thing for beautiful feet. In Mosiah 15:15-18, beautiful feet are mentioned four times.