This part now relates to our poor miserable life, which, although we have and believe the Word of God, and do and submit to His will, and are supported by His gifts and blessings is nevertheless not without sin. For we still stumble daily and transgress because we live in the world among men who do us much harm and give us cause for impatience, anger, revenge, etc. Besides, we have Satan at our back, who sets upon us on every side, and fights (as we have heard) against all the foregoing petitions, so that it is not possible always to stand firm in such a persistent conflict.
Therefore there is here again great need to call upon God and to pray: Dear Father, forgive us our trespasses. Not as though He did not forgive sin without and even before our prayer (for He has given us the Gospel, in which is pure forgiveness before we prayed or ever thought about it). But this is to the intent that we may recognize and accept such forgiveness. For since the flesh in which we daily live is of such a nature that it neither trusts nor believes God, and is ever active in evil lusts and devices, so that we sin daily in word and deed, by commission and omission by which the conscience is thrown into unrest, so that it is afraid of the wrath and displeasure of God, and thus loses the comfort and confidence derived from the Gospel; therefore it is ceaselessly necessary that we run hither and obtain consolation to comfort the conscience again.
But this should serve God's purpose of breaking our pride and keeping us humble. For in case any one should boast of his godliness and despise others, God has reserved this prerogative to Himself, that the person is to consider himself and place this prayer before his eyes, and he will find that he is no better than others, and that in the presence of God all must lower their plumes, and be glad that they can attain forgiveness. And let no one think that as long as we live here he can reach such a position that he will not need such forgiveness. In short, if God does not forgive without ceasing, we are lost.
It is therefore the intent of this petition that God would not regard our sins and hold up to us what we daily deserve, but would deal graciously with us, and forgive, as He has promised, and thus grant us a joyful and confident conscience to stand before Him in prayer. For where the heart is not in right relation towards God, nor can take such confidence, it will nevermore venture to pray. But such a confident and joyful heart can spring from nothing else than the [certain] knowledge of the forgiveness of sin.
But there is here attached a necessary, yet consolatory addition: As we forgive. He has promised that we shall be sure that everything is forgiven and pardoned, yet in the manner that we also forgive our neighbor. For just as we daily sin much against God and yet He forgives everything through grace, so we, too, must ever forgive our neighbor who does us injury, violence, and wrong, shows malice toward us, etc. If, therefore you do not forgive, then do not think that God forgives you; but if you forgive, you have this consolation and assurance, that you are forgiven in heaven, not on account of your forgiving, -- for God forgives freely and without condition, out of pure grace, because He has so promised, as the Gospel teaches, -- but in order that He may set this up for our confirmation and assurance for a sign alongside of the promise which accords with this prayer, Luke 6, 37: Forgive, and ye shall be forgiven. Therefore Christ also repeats it soon after the Lord's Prayer, and says, Matt. 6,14: For if ye forgive men their trespasses, your heavenly Father will also forgive you, etc.
This sign is therefore attached to this petition, that, when we pray, we remember the promise and reflect thus: Dear Father, for this reason I come and pray Thee to forgive me, not that I can make satisfaction, or can merit anything by my works, but because Thou hast promised and attached the seal thereto that I should be as sure as though I had absolution pronounced by Thyself. For as much as Baptism and the Lord's Supper appointed as external signs, effect, so much also this sign can effect to confirm our consciences and cause them to rejoice. And it is especially given for this purpose, that we might use and practise it every hour, as a thing that we have with us at all times.