Nephi’s final testimony appropriately reprises themes he has already taught. Most recently in chapter 31 he reiterated his love of plainness. The theme of anger against the true word of God has surfaced more than once (see 2 Nephi 1:26 and 2 Nephi 28:28 as examples).
Literary: the effect of Nephi’s declaration of the potential reaction to his words is to contrast the righteous with the wicked. Those with the true spirit of God will accept them, and those who are “of the devil” will become angry with them. Nevertheless, Nephi asserts their truthfulness with his own testimony of his personal salvation before the Lord.