Nephi prays for his people. His desire is that those prayers work for their salvation, that they persuade them to do good. In particular, he reemphasizes his constant theme of the coming atoning Messiah.
Nephi, as their teacher, has spoken “harshly against sin, according to the plainness of the truth.” Another truth he teaches is that those who have the spirit of God will accept correction, but those who have the spirit of the devil will reject the correction and be angry because of it. Regardless of the personal justification that they might make for their actions, their spirit will understand if they are contrary to God’s plan of happiness. Anger is the opposition to that happiness in God.
Nephi says that he speaks in plainness and reiterates that he glories in plainness. He has made things as clear as he can. He testifies of the Messiah because of his personal experience with the blessings of the Messiah.