Literary: It is tempting to see these verses as a type of chiasm, but the verses have a subtle change of reference that suggests that the third verse builds upon the first rather than simply reflect it.
In verse 21 the message is:
This is the first part of the prophecy, it begins with a people who are not in bondage, and offers them freedom from entering bondage by repenting.
Verse 22 appears to indicate the foreknowledge of God that they would not repent in time to spare themselves the bondage and afflictions. When they do not repent, the afflictions will come, and God declares himself behind them. As with other afflictions by God in the Old Testament, the rhetoric has God playing an active role in supplying the afflictions, when what is meant is that he allows others to perpetrate them.
In verse 23 Abinadi appears to return to the repentance theme. It is true that he returns to the theme, but the timing of the repentance is clearly different that that of verse 21. In verse 23 the message is:
While the language is parallelistic, the theme is progressive through time, with the final pronouncement indicating the foreknowledge of God that they will come under bondage and affliction. Even in that state, and with this perhaps pessimistic prophecy, yet the Lord still holds hope before the people of Noah. There is still room for repentance, and when they repent, the Lord will deliver them. The story of the public penance, repentance, and preparation for salvation we have already seen in the story of Ammon before Limhi.