The answer to “What do you teach?” is “We teach the law of Moses.” That should be uncontroversial. Abinadi certainly believes the scriptures, and certainly believes, as did Nephi and his religious descendants, that the Nephites should follow the law of Moses.
Abinadi does not argue against the law, but against the priests. He asks, “If ye teach the law of Moses why do ye not keep it?” What Abinadi declares as evidence that they do not keep the law of Moses, however, is not clearly a violation of the law of Moses. It is contrary to Nephite interpretation of the law, but not necessarily to the law. Still, as Abinadi noted, these were the things that he had condemned them for.
Note that Abinadi has also temporarily avoided explaining the verses from Isaiah. He is setting up a framework in which his answer can be provided and be seen as complementary to the scriptures, rather than as the assumption that the priests had, which was that Abinadi could not reconcile his teachings with those verses.
What Abinadi asks is about salvation, demonstrating that the reason for the verses was indeed the issue of salvation. He gets them to commit to the statement that “salvation did come by the law of Moses.”