Charles Ellicott Commentary Matthew 18:21

"Then came Peter and said to him, Lord, how oft shall my brother sin against me, and I forgive him? until seven times?" — Matthew 18:21 (ASV)

How oft shall my brother sin...? — The words of Matthew 18:15 had obviously affected the disciples, rousing them to question among themselves. But they could not immediately grasp the truth that the “commandment” was “exceeding broad.” Surely, they thought, there must be some limit to this way of dealing with the brother who has sinned against us?

And so the sacred number seven suggested itself as the natural limit. It may be conjectured that the Apostle, perhaps with a half-conscious reference to the prophet's words that for three transgressions and for four its punishment would not be turned away (Amos 1:3), answered his own question: Until seven times? He likely thought the line must be drawn there.