A confusing aspect of our Christian growth is that we can, sometimes even at the same moment, have a very peaceful, godly thought full of love for God and neighbour, and then have a terribly sinful and embarrassingly nasty thought. How can this be? If God is alive in us, how can such terrible thoughts keep appearing in our minds? How do we combat this?
One unhelpful way to combat this experience of good thoughts followed by bad thoughts is to become angry with ourselves, thinking that we must just try harder. Trying harder not to think bad thoughts only increases our bad thoughts.
A Father of the Philokalia, St. Diadochos of Photiki, said that our mind is like a man facing the rising sun on a cold winter morning. His face feels the warmth of the sun, but his back still feels the chill of the cold. Similarly, the Holy Spirit shining in our hearts warms our mind helping us to have thoughts of humility, thanksgiving and love for neighbour. However, because we have a habit of thinking wicked, judgemental and angry thoughts—like the cold of winter—we still feel and experience these ungodly thoughts.
So how do we increase the good thoughts and decrease the bad ones? Like the cold man in winter, we continue to face the sun. By paying attention to our thoughts that tend toward the fruit of the Spirit (love, joy, peace, patience, kindness, gentleness, goodness, faith, self control), we increase the warmth of God in ourselves. By paying attention to our wicked, angry, and judgemental thoughts and memories, we turn away from the sun, step into the shade—like Adam and Eve hiding in the fig trees—and thus our wicked thoughts increase. Our thoughts are a bit like muscles: the ones you exercise get bigger and stronger.
So what do you do with the bad thoughts? You ignore them. You don’t fight them or argue with them, you ignore them. One Desert Father said that arguing with a thought is like trying to drive a dog away by throwing biscuits at it. You are actually feeding the thought by arguing with it. If a nasty thought is so persistent that you can’t ignore it, then confess it to a priest, or a counsellor or a trusted spiritual friend (not to the person the thought is about!). It might be a bit shameful to confess, but confessing a persistent bad thought is one of the surest ways to deprive it of its power over you.
And most importantly, keep facing the sun. Keep nurturing those disciplines and activities that tend to produce the fruit of the Spirit, and work to avoid those activities or relationships or situations that stir up your passions. This is what the Church calls asceticism.