John Chrysostom

"Always bearing about in the body the dying of the Lord Jesus, that the life also of Jesus may be manifested in our body." And what is the "dying of the Lord Jesus," which they bare about? Their daily deaths by which also the resurrection was showed. 'For if any believe not,' he says, 'that Jesus died and rose again, beholding us every day die and rise again, let him believe henceforward in the resurrection.' Seest thou how he has discovered yet another reason for the trials? What then is this reason? …

Homily 9 on 2 Corinthians ↗

Theophylact of Ohrid

That is, by daily being subjected to death and always imitating the death of the Lord, we thus bear witness to His life, or to His resurrection, in our body. For if someone does not believe that the Lord rose, he will have no pretext for unbelief when he sees that we die daily and yet daily remain alive.

Commentary on 2 Corinthians ↗

Irenaeus

That he uses these words with respect to the body of flesh, and to none other, he declares to the Corinthians manifestly, indubitably, and free from all ambiguity: "Always bearing about in our body the dying of Jesus, that also the life of Jesus Christ might be manifested in our body. For if we who live are delivered unto death for Jesus' sake, it is that the life of Jesus may also be manifested in our mortal flesh."

Against Heresies Book V ↗

Thomas Aquinas

Then when he says, always carrying in the body the death of Jesus, he gives the reason for this patience. Here it should be noted that in Christ the process was this: having from the beginning of his conception a flesh that could suffer, he both suffered and died, yet within he was leading a spiritual life. But after the resurrection that spiritual and glorious life flowed into the body, so that his body became glorious and immortal, because "Christ being raised from the dead will never die again" (Rom. 6:9). …

Commentary on 2 Corinthians ↗