Who are the “some that have understood”? In the past, if someone has referred to a scripture, they have usually identified the prophet being quoted. This reference, in contrast, seems to allude to a form of scholarly debate with which Alma was familiar and which, because of the brief introduction, was apparently familiar to Corianton as well.
At issue is the process of the resurrection. Alma has already stated that the number of resurrections did not matter (v. 5), apparently because “some” saw the consciousness of the post-death spirit itself as a resurrection. Alma agrees that it does seem to resemble a resurrection but that it is, nevertheless, incorrect. In fact, it is not only incorrect but dangerous. Adherents of this belief could simultaneously declare themselves attached to the scriptures while still denying the Messiah because the resurrection had already occurred in the spirit’s survival of death. Thus, there would be no need for the future Messiah. Alma is not just arguing theology here, but dealing with the points that would have shaken Corianton’s faith.