A venial sin of your own is a greater obstacle to your experiencing the love of Jesus Christ than the sin of anyone else, however great it may be. It is clear, then, that you must harden your heart against yourself, humbling and detesting yourself more strongly for all the sins that hold you back from the vision of God than you detest the sins of others. For if your own heart is free from sin, the sins of others will not hurt you. Therefore, if you wish to find peace, both in this life and in heaven, follow the advice of one of the holy fathers, and say each day: "What am I?" and do not judge others.
Book I, ch. 16 (p. 18) - The Ladder of Perfection (1494)