Charles Spurgeon, Lectures to My Students:

Watch the twists and turns and singularities of your own mind, and the strangeness of your own experience; the depravity of your heart, and the work of divine grace; your tendency to sin, and your capacity for holiness; how akin you are to a devil, and yet how allied to God Himself! Note how wisely you can act when taught of God, and how foolishly you behave when left to yourself.