One of the most profound and life-changing things I've learned in my time at seminary is also one of the most remarkably simple things. I first heard it from a Benedictine nun, then discovered it in the writings of ancient Christian monastics and eventually realized that wise people from various faiths and cultures have taught it. Since learning it, I endeavor to apply it continuously to my own life and have found it to be true and utterly beneficial. It is this:

You are not your thoughts. Your thoughts are not you. 

You can step back and observe your thoughts. They pass through your consciousness like clouds across a sky. You can choose whether to entertain them or simply let them pass on by. They are temporary; ephemeral. Thoughts of anger, resentment, lust, hatred, self-loathing, jealousy, etc. only become sinful and harmful if you choose to engage them. But if you simply observe and acknowledge them and let them float on down the stream of consciousness, they cannot actualize and thus have no power.

Jesus taught that it is not what goes into a person that defiles them but what comes out of a person: "For out of the heart come evil thoughts—murder, adultery, sexual immorality, theft, false testimony, slander." (Matthew 5:19)

Rather than try to repress thoughts, or heap recrimination upon oneself for thoughts, one simply observes and releases. It actually takes discipline to let go and not engage; not entertain; not identify with the thought and thus allow it to arise out of the heart. The ancient Christian contemplatives called this practice of observing but not engaging one's thoughts "the guard of the heart."

The 17th century Quaker George Fox wrote, "After thou seest thy thoughts, and the temptations, do not think but submit; and then power comes. Stand still in that which shows and discovers; and there doth strength immediately come. And stand still in the light, and submit to it, and the other will be hushed and gone; and then content[ment] comes. And when temptations and troubles appear, sink down in that which is pure, and all will be hushed and fly away."

The Augustinian monk Martin Laird uses the analogy of looking out upon a canyon and observing weather patterns move across it--always changing, arising, dissipating, moving off over the horizon. The weather changes but the canyon remains.

You are not your thoughts. Your thoughts are not you.