1 Nephi 1:19

And it came to pass that the Jews did mock him because of the things which he testified of them; for he truly testified of their wickedness and their abominations; and he testified that the things which he saw and heard, and also the things which he read in the Book, manifested plainly of the coming of a Messiah, and also the redemption of the world.

The Jews made fun of him because of the things he told them about. He told them about their wickedness and sins. He told them that the things he saw and heard, and also the things he read in the book, showed clearly that a Messiah was coming and that the world would be saved.

The Jews mocked him for what he said. He told them straight about their evil and corruption. He testified that what he saw and heard—and what he read in that book—clearly showed a Messiah would come to save the world.