The resurrection, the joining of the spirit to the incorruptible body, will occur after Christ’s mortal mission. This is both true, and an admission that the time disjunction that has been part of the Corianton’s apostate argument is valid. There really is a difference in the timing. While Alma admits that point, he will reveal something more important.
What Alma tells us here is important beyond the specifics of resurrection that he will reveal. He tells us that we do not know all, and that some understandings are not simply given, but must be sought out. Notice that Alma gives Corianton the benefit of his own earnest searching: “I have inquired diligently of God that I might know.” We are in a similar position where there is much of the ways of God that is not clear. We may also inquire diligently. God does not present us with all knowledge simply because we are members of the church. Indeed, he does not simply present information to a prophet and leader as great as Alma. We, as individuals, must do as Alma did, and inquire diligently. The same reward of understanding can be available to us, but we are required to put forth the same kind of effort that Alma did.