1 The Holy Gospel which we heard just now as it was being read, has admonished touching the remission of sins. And on this subject must ye be admonished now by my discourse. For we are ministers of the word, not our own word, but the word of our God and Lord, whom no one serves without glory, whom no one despises without punishment. He then the Lord our God, who abiding with the Father made us, and having been made for us, re-made us, He the Lord our God Jesus Christ Himself says to us what we have heard just now in the Gospel.
“If,” He says, “your brother shall sin against you, rebuke him, and if he shall repent, forgive him; and if he shall sin against time seven times in a day, and shall come and say, I repent, forgive him.” He would not have “seven times in a day” otherwise understood than “as often as may be,” lest haply he sin eight times, and you be unwilling to forgive. What then is “seven times”? Always, as often as he shall sin and repent. For this, “Seven times in a day will I praise you,” is the same as in another Psalm, “His praise shall always be in my mouth.” And there is the strongest reason why seven times should be put for that which is always: for the whole course of time revolves in a circle of seven coming and returning days.
Source: Sermons on Selected Lessons of the New Testament (New Advent)