Matthew 18:21 - Ellicott's Commentary On The Whole Bible

How oft shall my brother sin...? — The words of Matthew 18:15 had obviously told on the minds of the disciples, and had roused them to question with themselves. But they could not, all at once, take in 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 the sacred number suggested itself as the natural limit. Not, it may be conjectured, without a half-conscious reference to the words of the prophet (Amos 1:3), that “for three transgressions and for four” the punishment thereof should not be turned away, the Apostle made answer to his own question, “Until seven times?” as though the line must be drawn there.