Various Excerpts On Forgiveness:

'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' (I Jn. 1:8), we lie, as John says...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.

St. Cyril of Jerusalem (Catechetical Lectures: Lecture 23 no. 16)

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Do we forgive our neighbors their trespasses? God also forgives us in His mercy. Do we refuse to forgive? God, too, will refuse to forgive us. As we treat our neighbors, so also does God treat us. The forgiveness, then, of your sins or unforgiveness, and hence also your salvation or destruction, depend on you yourself, man. For without forgiveness of sins there is no salvation. You can see for yourself how terrible it is.

St. Philotheos of Sinai

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No one is as good and kind as the Lord is; but He does not forgive one who does not repent.  

St. Mark the Ascetic

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Not only is it wonderful that He forgives us our sins, but also that He neither uncovers them nor does He make them stand forth clearly revealed. Nor does He force us to come forward and publicly proclaim our misdeeds, but He bids us to make our defense to Him alone and to confess our shins to Him. And yet, if any judge of a worldly tribunal were to tell some captured highwayman or grave robber to confess his crime and be excused from paying the penalty, this prisoner would with all alacrity admit the truth and scorn the disgrace in his desire to go free. But this is not the case in baptism. God forgives our sins and does not force us to make a parade of them in the presence of others. He seeks one thing only: that he who benefits by the forgiveness make learn the greatness of the gift.

St. John Chrysostom, ( Baptismal Instructions)

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Sometimes we do not see any outlet, any escape from our sins, and they torment us: on account of them, the heart is oppressed with sorrow and weary. But Jesus looks upon us, and streams of tears flow from our eyes, and with the tears all the tissue of evil in our soul vanishes. We weep with joy that such mercy has suddenly and unexpectedly been sent to us.

St. John of Kronstadt

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...it is impossible for a man to be freed from the habit of sin before he hates it, just as it is impossible to receive forgiveness before confessing his trespasses...  

Monks Callistus and Ignatius (Directions to Hesychasts no. 28, Writings from the Philokalia on Prayer of the Heart; Faber and Faber pg. 199)