Abinadi and Paul both express the relationship of the law of Moses to the law of the Gospel. Paul's statement
Gal. 3:24 "Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith."
Both of these statements are essentially the same, but the perspective is different. Paul's statement has a more positive connotation to it. The law was necessary, but it was simply a teacher, and the Gospel would bring a more important way. Abinadi's statement is less positive, casting the law as necessary for a "stiffnecked" people. His explanation of how it worked in relation to Christ's law is essentially, the same, however. This "law of performances and ordinances" allowed these "children" to learn slowly, with rigid instructions for each day. It is this rigidity of practice that would be replaced.
The difference in connotation comes form the situation in which both prophets give their explanations. Paul was trying to win over converts, and therefore placed the points of contiguity of belief in the best possible light. Abinadi, on the other hand, appears to have no expectation of conversion (though he makes one convert that justifies his entire mission). He is condemning. In particular, he is condemning a group of priests who are placing the law above the gospel of Christ. In that case, it is Abinadi's purpose to show that they are mistaken in removing Christ from their teachings, and therefore he must show that the law of Moses is not as powerful nor salvific as they preach.