William Burkitt on 2 Corinthians 11:24

The law in Deut 25:3 allowed forty stripes to be given to them that were worthy to be beaten, but forbade them to exceed that number: But it being their custom to beat them with a whip that had three cords, they must either stop at thirty-nine, or exceed and go to forty-two.

Here observe, That the apostle contending with these false teachers, proves the truth of his ministry and apostleship; not, as elsewhere, from the miracles and gifts of the Holy Ghost, which did accompany his preaching, but from his sufferings, as being the things which these false apostles could not pretend unto, and so could not glory that they were like unto him in them.