The Flesh and the Spirit

Obviously, the purpose of this mortal life is to be prepared for the next: immortal life. God conceives within us His nature. That is what makes us the children of God. With His help, we bring the attributes of that nature to fruition, guaranteeing that when born into the spirit realm we will never sin (1 John 3:9), will never rebel against God as did one third of the angels. Angels did not experience a preliminary, preparatory existence as humans do. Yet, until our dying breath, we remain sinners (1 John 1:8). What then becomes of that tendency to sin once we are made alive at Christ's return?