16 And forgive us our debts as we also forgive our debtors. For we have many sins. For we offend both in word and in thought, and very many things we do worthy of condemnation; and if we say that we have no sin, we lie, as John says. And we make a covenant with God, entreating Him to forgive us our sins, as we also forgive our neighbours 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. Take heed therefore, lest for the slight and trivial sins against you, you shut out for yourself forgiveness from God for your very grievous sins.
Source: Catechetical Lectures (New Advent)