The prayer of one who does not consider himself a sinner is not accepted by the Lord.
Isaac of NinevehLet there always be a preponderance of mercy with you, even though you don't feel such mercy in yourself, as God has for the world ... A cruel and merciless heart is never purified. A merciful man is the doctor of his own soul, because as it were a by a strong wind from is heart he drives out the darkness of the passions.
Isaac of NinevehWithout temptations, it is not possible to learn the wisdom of the Spirit. It is not possible that Divine love be strengthened in your soul. Before temptations, a man prays to God as a stranger. When temptations are allowed to come by the love of God, and he does not give in to them, then he stands before God as a sincere friend. For in fulfilling the will of God, he has made war on the enemy of God and conquered him.
Isaac of NinevehLove sinners, but hate their deeds, and do not disdain sinners for their failings, so that you yourself do not fall into the temptation in which they abide... Do not be angry at anyone and do not hate anyone, neither for their faith, nor for their shameful deeds... Do not foster hatred for the sinner, for we are all guilty... Hate his sins, and pray for him, so that you may be made like unto Christ, who had no dislike for sinners, but prayed for them.
Isaac of Nineveh