We have seen, heard, and handled that which was from the beginning, the word of life. (1 John 1:1)
Now that is a strange way to start a letter. It doesn't say who is writing the letter, or who it is addressed to. But it does sound a lot like the way the gospel of John began - and the rest of 1 John sounds similar, as do 2 and 3 John. So these three epistles are called the Johannine epistles, since they sound as if they might have been written by the same person who wrote John's Gospel. But since the Gospel of John and the three Johannine epistles are anonymous, we don't know who the author (or authors) of any of them are. Wikipedia: Authorship of the Johannine works
You've heard that the antichrist will come. Now there are many antichrists, so we know the end is here. (1 Jon 2:18)
The word "antichrist" is only mentioned five times in the Bible. Twice in this verse, two other times in 1 John (2:22, 4:3) and in 2 John 7.
An antichrist, according to these verses, is anyone who denies that Jesus has come in the flesh, or who denies that he is the Messiah, or who denies the Father and the Son, or who is a former believer. The term is not used in the book of Revelation.
There are three that bear witness in heaven: the Father, the Word, and the Holy Ghost. And these three are one. (1 John 5:7)
This is the clearest, and pretty much the only, expression of the Trinitarian concept in the Bible. It is not, however, found in the earliest Greek manuscripts and is omitted from most modern translations. Here, for example, are verses 7-8 in the New Revised Standard Version: "There are three that testify: the Spirit and the water and the blood, and these three agree."
Not all Christians agree about how these verses (often called the Johannine comma) should be treated. See here for a KJV-only defense.
