Inserted into Alma's discourse against kings is a brief statement about his own process of conversion. These verses are interesting both for what they say, and for where they are said.
What the verses say is that Alma required repentance. He was not able to simply hear Abinadi, and immediately say "Whoops - I think I'll follow Abinadi now." Alma was not immediately transformed, but endured "sore repentance" (verse 9). What we learn is that after Alma escaped from the palace during Abinadi's trial, he underwent a trial of his own before God. Alma recognized himself as being contrary to God's will, understood the gravity of his actions, and desired change. This is the process of repentance. We do not know what he was required to do, but certainly the effect upon his soul was tremendous. He describes his conversion as a "sore" repentance, requiring "much tribulation." This process, however, did transform Alma, and the disfavor the Lord might have expressed that led to the "sore repentance" and "much tribulation" turned into approval of the converted Alma, in that the Lord allowed Alma to be the instrument in the Lord's hands for teaching these who also hearkened to the message of Abinadi (through Alma).
The second aspect of these verses that is interesting is where they are placed in the text. These verses on the repentance of Alma are given not only during the discourse against kingship, but as a part of the discourse against kingship. The repentance was from the Lord, but the need for repentance came from the excesses of kingship. Where Alma has previously denounced kingship for the social stratification, he now attacks the harmful effects of a king who has lost his way with God.
Once again it must be emphasized that ancient kingship was equally religious and political. As the religious leader, king Noah had the responsibility to lead his people to God, and instead he led them away. Alma is not just inserting his story here for sympathy, but rather as another example of the dangers of kingship - the spiritual dangers in addition to the social ones he earlier elaborated upon.