2 Corinthians 5:4

4.We groan, being burdened, because we desire not to be unclothed. The wicked, too, groan, because they are not contented with their present condition; but afterwards an opposite disposition prevails, that is, a clinging to life, so that they view death with horror, and do not feel the long continuance of this mortal life to be a burden. The groaning of believers, on the other hand, arises from this — that they know, that they are here in a state of exile from their native land, and that they know, that they are here shut up in the body as in a prison. Hence they feel this life to be a burden, because in it they cannot enjoy true and perfect blessedness, because they cannot escape from the bondage of sin otherwise than by death, and hence they aspire to be elsewhere.

As, however, it is natural for all animals to desire existence, how can it be, that believers are willing to cease to exist? The Apostle solves this question, when he says, that believers do not desire death for the sake of losing any thing, but as having regard to a better life. At the same time, the words express more than this. For he admits, that we have naturally an aversion to the quitting of this life, considered in itself, as no one willingly allows himself to be striped of his garments. Afterwards, however, he adds, that the natural horror of death is overcome by confidence; (515) as an individual will, without any reluctance, throw away a coarse, dirty, threadbare, and, in one word, tattered garment, with the view of his being arrayed in an elegant, handsome, new, and durable one.

Farther, he explains the metaphor by saying —

that what is mortal may be destroyed (516) by life. For as flesh and blood cannot inherit the kingdom of God,
(1 Corinthians 15:50,)

it is necessary, that what is corruptible in our nature should perish, in order that we may be thoroughly renewed, and restored to a state of perfection. On this account, our body is called a prison, in which we are confined.