Just an interesting section I took from this while doing some research!

“The fundamental insight shared by the ancient philosophers like Plato and by Christ is that an interior discipline of thoughts is needed. The only way to avoid bad actions and promote happiness is to go deeper than the actions themselves and to train our thoughts.

This deep human insight is expressed by Jesus with imaginative force in the Sermon on the Mount: (Matthew’s Gospel 5: 21-22 and 27-28)

You were told ‘do not kill’ and that if you do kill you will answer for it before the court. But I say anyone who is angry with another person will answer for it before the court. 

You were told ‘do not commit adultery’ but I say that if you look at a person lustfully, you have already committed adultery with them in your heart.

This is not Jesus simply creating impossibly high standards; he is saying that anger and lust are the origins of murder and adultery so get a hold of them before it is too late. As a society, we seem to have forgotten this very simple insight.”

—Abbot Christopher Jamison (“Spiritual Apathy: The Forgotten Deadly Sin”)