After noting that his soul delighted in the words of Isaiah, Nephi takes the theme of delight and expands it. Thus there are three additional things in which his soul delighted: the truth of the coming of Christ; the covenants between Jehovah and the fathers, meaning Israel; and the grace and justice of Jehovah, as manifest in his “great and eternal plan of deliverance from death.”
Each of these things picks up on a theme from Jacob’s sermon that was just concluded. Thus, Nephi is bearing testimony of the things Jacob said. The longest explanation is for the truth of the coming of Christ, where he elaborates on what Jacob had said. Jacob spoke of the prophesied mortal mission of the Messiah, and Nephi expands the topic to include all prophets, and indeed the law itself, which typify and therefore testify of the mortal Messiah, or Jehovah in his mortal mission.