Jamieson, Fausset and Brown on Genesis 32:31

31. halted upon his thigh--As Paul had a thorn in the flesh given to humble him, lest he should be too elevated by the abundant revelations granted him [2Co 12:7], so Jacob's lameness was to keep him mindful of this mysterious scene, and that it was in gracious condescension the victory was yielded to him. In the greatest of these spiritual victories which, through faith, any of God's people obtain, there is always something to humble them.