John Calvin Commentary Genesis 32:25

"And when he saw that he prevailed not against him, he touched the hollow of his thigh; and the hollow of Jacob`s thigh was strained, as he wrestled with him." — Genesis 32:25 (ASV)

And when he saw that he prevailed not against him. Here, the victory of Jacob is described to us, which, however, was not gained without a wound. In saying that the wrestling angel, or God, wished to withdraw from the contest because He saw He would not prevail, Moses speaks in human terms. For we know that God, when He descends from His majesty to us, is accustomed to attribute human characteristics to Himself. The Lord knew with certainty the outcome of the contest before He came down to engage in it; He had even already determined what He would do. But His knowledge is here presented as the experience of the event itself.

He touched the hollow of his thigh. Though Jacob gains the victory, yet the angel strikes him on the thigh, which caused him to be lame for the rest of his life. And although the vision was by night, the Lord designed this mark of it to continue throughout all his days, so that it would thereby be apparent that it had not been a vain dream. Moreover, by this sign it is made clear to all the faithful that they can emerge as conquerors in their temptations only by being injured and wounded in the conflict.

For we know that the strength of God is made perfect in our weakness, so that our exaltation may be joined with humility. For if our own strength remained intact, and no injury or dislocation occurred, the flesh would immediately become haughty, and we would forget that we had conquered by God's help. But the wound received, and the weakness that follows it, compel us to be modest.