Rhetorical: Alma is using a device that shows a contradiction that the audience can see, but may not be able to see the solution. Such a presentation of a problem piques the interest of an audience so that they might better follow the argument.
In Alma's discourse, the contrast between verses 15 and 16 set the stage for the problem that Alma will resolved. He has noted that the wicked will stand before God, and be afraid. In verse 15 he notes that this isn't what is supposed to happen. What should happen is that we stand before him and acknowledge him, not run from him. What makes the difference? That is what Alma will discuss.