St. Cyril of Jerusalem
“We make a covenant with God, entreating Him to forgive us our sins, as we also forgive our neighbors their debts. Considering then what we receive and in return for what, let us not put off nor delay to forgive one another. The offenses committed against us are slight and trivial, and easily settled; but those which we have committed against God are great, and need such mercy as His only is.”
Source: St. Cyril of Jerusalem, Catechetical Lectures