Textual: These verses come at the end of Mormon’s moral story which justifies Abinadi’s prophecy. In verse 10 above Mormon cites Abinadi’s words, and so it is reasonable to presume that he was consulting either his sources for Abinadi’s speech, or his own record of that speech when this section was written. With that understanding, we may therefore suspect that what was written in the account of Abinidi has directly influenced these two verses. Note the similarities with a declaration by Abinadi:
Mosiah 13:27-33
27 And now ye have said that salvation cometh by the law of Moses. I say unto you that it is expedient that ye should keep the law of Moses as yet; but I say unto you, that the time shall come when it shall no more be expedient to keep the law of Moses.
28 And moreover, I say unto you, that salvation doth not come by the law alone; and were it not for the atonement, which God himself shall make for the sins and iniquities of his people, that they must unavoidably perish, notwithstanding the law of Moses.
29 And now I say unto you that it was expedient that there should be a law given to the children of Israel, yea, even a very strict law; for they were a stiffnecked people, quick to do iniquity, and slow to remember the Lord their God;
30 Therefore there was a law given them, yea, a law of performances and of ordinances, a law which they were to observe strictly from day to day, to keep them in remembrance of God and their duty towards him.
31 But behold, I say unto you, that all these things were types of things to come.
32 And now, did they understand the law? I say unto you, Nay, they did not all understand the law; and this because of the hardness of their hearts; for they understood not that there could not any man be saved except it were through the redemption of God.
33 For behold, did not Moses prophesy unto them concerning the coming of the Messiah, and that God should redeem his people? Yea, and even all the prophets who have prophesied ever since the world began—have they not spoken more or less concerning these things?
We have not only the same theme, but also some of the same language in Alma that we do in Mosiah 13. In both it is “expedient to keep the law of Moses.” The justification for keeping the law of Moses is then set into the context of a preparation for the coming of Christ. The similarities between the two passages and the proximity to a reference to Abinidi suggest that the verses in Alma are related to those in Mosiah.