From John Piper…
Though our outer self is wasting away, our inner self is being renewed day by day.(2 Corinthians 4:16)
Paul can’t see the way he used to (and there were no glasses). He can’t hear the way he used to (and there were no hearing aids). He doesn’t recover from beatings the way he used to (and there were no antibiotics). His strength, walking from town to town, doesn’t hold up the way it used to. He sees the wrinkles in his face and neck. His memory is not as good. And he admits that this is a threat to his faith and joy and courage.
But he doesn’t lose heart. Why?
He doesn’t lose heart because his inner man is being renewed. How?
The renewing of his heart comes from something very strange: it comes from looking at what he can’t see.
We look not to the things that are seen but to the things that are unseen. For the things that are seen are transient, but the things that are unseen are eternal. (2 Corinthians 4:18)
This is Paul’s way of not losing heart: looking at what you can’t see. What did he see?
A few verses later in 2 Corinthians 5:7, he says, “We walk by faith, not by sight.” This doesn’t mean that he leaps into the dark without evidence of what’s there. It means that for now the most precious and important realities in the world are beyond our physical senses.
We “look” at these unseen things through the gospel. We strengthen our hearts — we renew our courage — by fixing our gaze on the invisible, objective truth that we see in the testimony of those who saw Christ face to face.