Apparently, there had been some confusion in Alma’s day about the status of spirits and the time of judgment in post-mortal life. The assignment to paradise, for example, is a judgment based our earthly lives: what ordinances we have received, how we have used our stewardship, etc. Alma refers to that as the “consignation to happiness or misery.” This, he points out, is not to be confused with the first resurrection, which refers to the time when a first group of spirits are resurrected.
Alma reinforced the idea that, although the consignation to happiness and misery is a form of preliminary judgment, that is not the same as “the first resurrection,” nor does the resurrection occur for all people at the same time. As Alma said, people do not all die at the same time (40:8), so why do they need to be resurrected at the same time? We do not know how that will happen, or when it will happen, but eventually these points of judgment will occur.