Alma now begins with the solution, which is the Atonement. The first problem of temporal death is resolved in the Atonement. While all men must die, the atonement allows for them to be resurrected. This aspect of the Fall is redeemed. It is after this physical redemption, however, that the second aspect comes to play.
To this point, Alma has simply returned to his original statement, that a man might live forever after the resurrection. What Antionah was emphasizing was the problem of sin, a natural question for one of the order of Nehor, as one of their tenets was to deny that there was sin.