(1260 - 1328)
In fact, to have sinned is no sin if one regrets it. One should not wish to commit a sin for all that can happen in time or eternity - neither mortal nor venial nor any kind of sin. He who is wise in the ways of God should ever consider that our faithful and loving God has brought us from a sinful life to a godly life: out of an enemy He has made a friend, which is more than to have created a new earth. This should be one of the main reasons why one should establish oneself firmly in God, and it would amaze you how greatly this would inspire people in strong deep love, so that they would renounce themselves completely.
Indeed, a person truly established in God's will should not wish that the sin into which he had fallen had never been: not in the sense that it was against God, but because thereby you are bound to greater love and thus made lowly and humble - even though it was against God. But you should safely trust God not to have permitted this unless He wanted to turn it to your profit. But when a person stands right above sin and turns completely away, then our faithful God acts as if that man had never fallen into sin, and will not let him suffer for a moment for all his sins. Even if they were as many as all people have ever committed, God will never punish him, but would be as familiar to that person as to any other creature. Provided He finds him now ready, He pays no regard to what he was before. God is a God of the present. As He finds you, so He takes and receives you, not as what you were but as what you are now. All the harm and shame that God can bear on account of all sins, He will gladly bear and have borne for many a year, so that a person may come to a greater recognition of His love, and so that that person's love and gratitude may be the greater, and his zeal the hotter, as indeed is the right and frequent outcome after one has sinned.
That is why God gladly accepts the harm of sins and has often tolerated it and allowed it to come to those whom He has chosen to prepare for great things. See: who was dearer to our Lord or more intimate with him than the Apostles were? Yet not one of them but fell into mortal sin: they had all been mortal sinners. He has frequently shown this in both the Old and the New Testament in regard to those who afterwards were by far the dearest to Him; and even now one seldom finds that people come to greatness without erring somewhat at first. Our Lord's intention in this is that we should recognise his great mercy: he wants to urge us by this to great and true humility and devotion. For when repentance is renewed, love too is greatly increased and renewed.
Talks of Instruction, no. 12