Morning Prayer begins with an opening sentence and plunges immediately into confession. Its comprehensive and leaves no wiggle room or does it? The first sentence reads “Most merciful God, we confess that we have sinned against you in thought, word, and deed, by what we have done, and by what we have left undone.” Sins of deed are fairly easy to identify. We know what we did or didn’t do. Likewise we know what we have said. We are often also aware of our impure thoughts. Here’s the thing though. Not all impure thoughts are sinful.
Sometimes impure and even evil thoughts pop into our minds. This is not sin. This is temptation. Say for example you notice a particularly attractive man or woman. This is not sin. This is the equivalent of noticing a particularly beautiful sunrise or sunset. You admire the beauty. No problem here. If you stare and make the person uncomfortable you lack couth, but are still not sinning against God. Now if you notice such a person and begin to pencil out an action plan to have sex with them that is sin.
But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart. (Matthew 5:28 ESV)
Intent is the key here. St. Augustine famously described three stages of Sin: Suggestion, Pleasure, and Consent. A thought that comes into our minds is a Suggestion. It is not sin though it can tempt us towards sin. The thought can give us pleasure and our risk level rises as we enjoy the pleasure. This is when the temptation begins to take hold in our hearts and minds. Here we are in peril and the longer we entertain the pleasure the greater our risk becomes. When we welcome the pleasure, we have consented to it. We have surely sinned in thought.
Turning from thoughts before the pleasure grows is the key to resisting temptation and avoiding sin. Sins of thought that are allowed to grow become sins of word and deed. Jesus was unimpressed with people who avoided sins of deed but took no care for their interior life.
“Woe to you, scribes and Pharisees, hypocrites! For you clean the outside of the cup and the plate, but inside they are full of greed and self-indulgence." (Matthew 23:25 ESV)
When Jesus declared all food clean he said
"But what comes out of the mouth proceeds from the heart, and this defiles a person. For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander." (Matthew 15:18-19 ESV)
When we give consent to impure thoughts we sin and our hearts are twisted out of shape. What then shall we do? We repent and confess “Most merciful God, we confess that we have sinned against you in thought, word, and deed, by what we have done, and by what we have left undone.” When impure thoughts arise unbidden turn from them as quickly as you are able. It is when we entertain pleasure and give consent that it becomes a habit and harder to resist. We can feel powerless. This feeling is part of the fruit of sin. We are not powerless. We have God on our side. Our Lord is quick to forgive and offers grace to strengthen us. Put forth the Cross as your shield against temptation. Consider again the words of Hippolytus
“When tempted, always reverently seal your forehead with the Sign of the Cross. For this sign of the Passion is a symbol openly combatting the devil if you make it in faith, not in order that you may be seen by others, but consciously putting it forth like a shield.” (Hippolytus c. 170–c. 236)
Where sin has taken root in your life this will be difficult at first. You will need to grow in character by persistently struggling to resist temptation. It is far easier to end a temptation before sin becomes a habit than to rid oneself of the sin. If you've read the Narnia Chronicles consider Eustace in Voyage of the Dawn Treader.
May God have mercy upon us and forgive us all our sins.