In previous verses, Nephi declared that the great and abominable church must be brought down. These verses expand on that which the great and abominable church teaches that must be reversed.
The first, in verse 20, is that it will stir up the children of men “to anger against that which is good.” This alludes to Isaiah 5:20: “Woe unto them that call evil good, and good evil.”
The second, in verse 21, is that humankind will be lulled into a false sense of security. This returns to Nephi’s earlier statement that “God will beat us with a few stripes, and at last we shall be saved” (quoted from verse 8 in this chapter).
Next, in verse 22, we have mention of teaching that “there is no hell.” Although the idea of hell is a later development, the idea that there is a punishment for the wicked is appropriate for Nephi’s time. Thus, the issue is whether or not there are consequences for our actions. Nephi declares that there are, and thus there is danger in the false teaching that there are no such consequences.
Those consequences are defined in verse 23. There is a place prepared for those who are opposed to God. Nephi has used the word devil to indicate an entity antithetical to God, and thus the consequences listed represent the opposite of the rewards awaiting those who are truly faithful to God.