Catechism of the Catholic Church
2838 This petition is astonishing. If it consisted only of the first phrase, "And forgive us our trespasses," it might have been included, implicitly, in the first three petitions of the Lord's Prayer, since Christ's sacrifice is "that sins may be forgiven." But, according to the second phrase, our petition will not be heard unless we have first met a strict requirement. Our petition looks to the future, but our response must come first, for the two parts are joined by the single word "as."
2839 With bold confidence, we began praying to our Father. In begging him that his name be hallowed, we were in fact asking him that we ourselves might be always made more holy. But though we are clothed with the baptismal garment, we do not cease to sin, to turn away from God. Now, in this new petition, we return to him like the prodigal son and, like the tax collector, recognize that we are sinners before him. 133 Our petition begins with a "confession" of our wretchedness and his mercy. Our hope is firm because, in his Son, "we have redemption, the forgiveness of sins." 134 We find the efficacious and undoubted sign of his forgiveness in the sacraments of his Church. 135
2840 Now - and this is daunting - this outpouring of mercy cannot penetrate our hearts as long as we have not forgiven those who have trespassed against us. Love, like the Body of Christ, is indivisible; we cannot love the God we cannot see if we do not love the brother or sister we do see. 136 In refusing to forgive our brothers and sisters, our hearts are closed and their hardness makes them impervious to the Father's merciful love; but in confessing our sins, our hearts are opened to his grace.
2841 This petition is so important that it is the only one to which the Lord returns and which he develops explicitly in the Sermon on the Mount. 137 This crucial requirement of the covenant mystery is impossible for man. But "with God all things are possible." 138
2842 This "as" is not unique in Jesus' teaching: "You, therefore, must be perfect, as your heavenly Father is perfect"; "Be merciful, even as your Father is merciful"; "A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another." 139 It is impossible to keep the Lord's commandment by imitating the divine model from outside; there has to be a vital participation, coming from the depths of the heart, in the holiness and the mercy and the love of our God. Only the Spirit by whom we live can make "ours" the same mind that was in Christ Jesus. 140 Then the unity of forgiveness becomes possible and we find ourselves "forgiving one another, as God in Christ forgave" us. 141
2843 Thus the Lord's words on forgiveness, the love that loves to the end, 142 become a living reality. The parable of the merciless servant, which crowns the Lord's teaching on ecclesial communion, ends with these words: "So also my heavenly Father will do to every one of you, if you do not forgive your brother from your heart." 143 It is there, in fact, "in the depths of the heart," that everything is bound and loosed. It is not in our power not to feel or to forget an offense; but the heart that offers itself to the Holy Spirit turns injury into compassion and purifies the memory in transforming the hurt into intercession.
2844 Christian prayer extends to the forgiveness of enemies, 144 transfiguring the disciple by configuring him to his Master. Forgiveness is a high-point of Christian prayer; only hearts attuned to God's compassion can receive the gift of prayer. Forgiveness also bears witness that, in our world, love is stronger than sin. The martyrs of yesterday and today bear this witness to Jesus. Forgiveness is the fundamental condition of the reconciliation of the children of God with their Father and of men with one another. 145
2845 There is no limit or measure to this essentially divine forgiveness, 146 whether one speaks of "sins" as in Luke (11:4), "debts" as in Matthew (6:12). We are always debtors: "Owe no one anything, except to love one another." 147 The communion of the Holy Trinity is the source and criterion of truth in every relation ship. It is lived out in prayer, above all in the Eucharist. 148
God does not accept the sacrifice of a sower of disunion, but commands that he depart from the altar so that he may first be reconciled with his brother. For God can be appeased only by prayers that make peace. To God, the better offering is peace, brotherly concord, and a people made one in the unity of the Father, Son, and Holy Spirit. 149
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.