I told the brethren that the Book of Mormon was the most correct of any book on earth, and the keystone of our religion, and a man would get nearer to God by abiding by its precepts, than by any other book. Joseph Smith, History of the Church, 4:461
They are wicked and filled with abominations (because they mocked Jesus)
The Jews did mock him because of the things which he testified of them; for he truly testified of their wickedness and their abominations. 1 Nephi 1:19
They are the most wicked people on earth. No one else would crucify their God.
The Jews, among those who are the more wicked part of the world; and they shall crucify him -- for thus it behooveth our God, and there is none other nation on earth that would crucify their God. 2 Nephi 10:3
Their works are works of darkness and they do abominations.
The Jews; for their works were works of darkness, and their doings were doings of abominations. 2 Nephi 25:2
For I, Nephi, have not taught them many things concerning the manner of the Jews; for their works were works of darkness, and their doings were doings of abominations. 2 Nephi 25:10
They are stiff-necked people, who despise plain words, killed the prophets, and tried to understand things that they couldn't understand. God has taken away their plainness and made them stumble.
But behold, the Jews were a stiffnecked people; and they despised the words of plainness, and killed the prophets, and sought for things that they could not understand. Wherefore, because of their blindness, which blindness came by looking beyond the mark, they must needs fall; for God hath taken away his plainness from them, and delivered unto them many things which they cannot understand, because they desired it. And because they desired it God hath done it, that they may stumble. Jacob 4:14
But someday they'll believe in Jesus and become a delightsome people.
And it shall come to pass that the Jews which are scattered also shall begin to believe in Christ; and they shall begin to gather in upon the face of the land; and as many as shall believe in Christ shall also become a delightsome people. 2 Nephi 30:7