One man was there who had been an invalid for thirty-eight years.
Verse 3 mentioned a multitude of disabled people. But here in verse 5 the focus is on but one of them. This is the convergence of an eternal God’s divinely orchestrated plan with its manifestation in time. This one man was the present purpose. Jesus could have healed all of them. But he signaled out just one.
John switches tense (one man was there) which again emphasizes the current reality of the temple’s present existence at the time of the Gospel’s writing.
The word for invalid is astheneia which means weakness, frailty, without strength, etc. There are passages, like this, which seem to be speaking of the weakness of the body, and others where it’s referring to the soul. For instance:
I am speaking in human terms, because of your natural limitations. For just as you once presented your members as slaves to impurity and to lawlessness leading to more lawlessness, so now present your members as slaves to righteousness leading to sanctification. (Romans 6.19)
Likewise the Spirit helps us in our weakness. (Romans 8.26)
If I must boast, I will boast of the things that show my weakness. (2Cor. 11.30)
The man’s age is not given. He could have been disabled from birth, or perhaps much later. In fact, very little details are given about this man other than his disability.From verse 7 and verse 8 we know the disability had something to do with the man’s ability to get up or walk. Verse 7 indicates he is able to move to some degree (or be moved), but not sufficiently fast enough to get into the pool before anyone else.
Thirty-eight years. That’s a long time. Perhaps we’re told the length of time to reveal just how bad this man’s situation was. We aren’t told how long he’s been at the pool, only the length of his infirmity, but verse 6 does indicate that he had “been there a long time”. I interpret this to refer to the length of time at the pool, not the length of time of his disability.