On the last day, our bodies will rise in the likeness of Christ & be united to our souls, nevermore to be separated. We shall either rejoice in glory in body & soul or suffer eternally in body & soul. Since we have become like unto God, who is in heaven in both body & soul, what more fitting way for us to spend eternity with him than by imitating the Resurrection of His body?
Now Christ rose again of youthful age, which begins about the age of thirty years, as Augustine says (De Civitate Dei xxii). Therefore others also will rise again of a youthful age. Further, man will rise again at the most perfect stage of nature. Now human nature is at the most perfect stage in the age of youth. Therefore all will rise again of that age… Man will rise again without any defect of human nature, because as God founded human nature without a defect, even so will He restore it without defect. Now human nature has a twofold defect. First, because it has not yet attained to its ultimate perfection. Secondly, because it has already gone back from its ultimate perfection. The first defect is found in children, the second in the aged: and consequently in each of these human nature will be brought by the resurrection to the state of its ultimate perfection which is in the youthful age, at which the movement of growth terminates, and from which the movement of decrease begins.” -St. Thomas Aquinas
“This body shall be raised, not remaining weak as it is now; it this same body shall be raised. By putting on incorruption it shall be altered, as iron bending with fire becomes fire – or rather, as the Lord who raises us knows. However it be, this body shall be raised, but it shall not remain such as it is; rather, it shall abide as an eternal body. It shall no longer require for its life such nourishment as now, nor shall it require a ladder for its ascent; for it shall be made a spiritual body, a marvelous thing, such as we have not the ability to describe. ‘Then shall the just,’ it is said, ‘shine forth like the sun and the moon, and like the spender of the firmament.’ And knowing beforehand the disbelief of man, God has caused little worms in the summer to emit beams of light from their bodies, so that from the things seen that which is awaited might be believed. He that gives the part is able also to give the whole; and He that made the worm radiant with light will much more be able to make radiant a righteous man. We shall be raised, then, all having eternal bodies, but not all with bodies alike. If a man is righteous, he shall receive a heavenly body, so that he may be able to converse worthily with the angels. But if a man is sinful, he shall receive an eternal body fitted to endure the penalties of sins, so that he may burn in the eternal fire without ever being consumed. And justly will God assign to those of either group their portion; for we do nothing without the body. We blaspheme with the mouth; with the mouth we pray. We fornicate with the body; with the body we are chaste. We rob with the hand; with the hand be bestow alms; and the rest in like manner. Since in all things the body has been our agent, it too shall in the future share in the fruits of what has been done.” -St. Cyril of Jerusalem