Here is Luther on the Fifth Petition in the Lord's Prayer. It is taken from the Large Catechism. I hope that you find it edifying:
"And forgive us our trespasses, as we forgive those who trespass against us"
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.