Alma specified that after the resurrection, we will be brought to stand before God with our bodies and be judged (Alma 40:21). Before that, there will be a level of judgment that will determine where people will reside in the spirit world, but the final judgment comes after our spirits and bodies are reunited (40:21). Thus, according to doctrine in the Book of Mormon, after resurrection, when we will stand before God to be judged, we must appear with and in our bodies. Thus, the Book of Mormon sees a need to return and report with our bodies to be judged according to the things that we have done in our bodies. For example, as Jacob said:
O how great the plan of our God! For on the other hand, the paradise of God must deliver up the spirits of the righteous, and the grave deliver up the body of the righteous; and the spirit and the body is restored to itself again, and all men become incorruptible, and immortal, and they are living souls, having a perfect knowledge like unto us in the flesh, save it be that our knowledge shall be perfect. Wherefore, we shall have a perfect knowledge of all our guilt, and our uncleanness, and our nakedness; and the righteous shall have a perfect knowledge of their enjoyment, and their righteousness, being clothed with purity, yea, even with the robe of righteousness (2 Nephi 9:13–14).
We will know then that the judgment given to us is just, because we will remember perfectly, both physically and spiritually, as is somehow necessary. (If we have repented, of course, we will not have a recollection of those sins and the Lord will remember them no more. This may mean that some of us may not have much to remember on that occasion, if we have repented well enough!) But, how we know and what we know must somehow be embedded in our physical makeup. In another setting, the Doctrine and Covenants similarly says that knowledge—the degree of intelligence that we have attained to in this life—will rise with us in the resurrection (130:18). This is the good news that Alma wanted Corianton to recognize. But with it comes the corresponding bad news that the same degree of darkness and error that we have attained to in this life will rise with us also, unless we have by that point in time truly repented.