Saint Gregory Nazianzus said that the immortality of an immoral body means the propagation of evil. In the mind of God, the immortality of the body is a way for the perfection of life. The fall of man had proved that this gift was not beneficial and that man had to perfect himself through pain. So after the Resurrection, we were introduced to the new way of perfection. Man had to be perfected spiritually first, than bodily.
Ethical perfection ought to precede bodily perfection as an assurance.
In other words we have to rise first spiritually, so that God bestows on us the Resurrection of the body. We have to be spiritually renewed so that spiritual bodies be given to us. The Resurrection of Christ is a strong proof that we will be given these spiritual bodies, but what is asked from us now is to offer spiritual perfection. Before the spiritual body, we need to have spiritual perfection. The Resurrection of Christ is a pledge of this spiritual body.