The Gospel teaches us to cut off the roots of our sins and not merely their fruits. When we have dug the root of anger out of our heart, we will no longer act with hatred or envy. 'Whoever hates his brother is a murderer' (I Jn. 3:15), for he kills him with the hatred in his mind. The blood of a man who has been slain by the sword can be seen by men, but blood shed by the hatred in the mind is seen by God, Who rewards each man with punishment or a crown not only for his acts but for his thoughts and intentions as well.
St. John Cassian