Catechism of the Catholic Church

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