He said, “That which proceeds out of the man, that defiles the man. – Mark 7:20

A Roman once said he wished he had a window to his heart, that all people might see what was going on there. I am very glad I have not; if I had I would shut it up as closely as Apsley House used to be; I would take care to have all the shutters up. Most of us would have great need of shutters if we had such a window. However, for one moment, peep into the window of thine heart, to observe what is there. Sin is there-original sin and corruption; and what is more, self is still within. Ah! if thou hadst no devil to tempt thee, thou wouldest tempt thyself; if there were no enemies to fight thee, thyself would be thy worst foe; if there were no world, still thy self would be bad enough; for “the heart is deceitful above all things, and desperately wicked.” Look within thee, believer; know that thou bearest a cancer in thy very vitals; that thou carriest within thee a bomb-shell, ready to burst at the slightest spark of temptation; know that thou hast inside thy heart an evil thing, a coiled-up viper, ready to sting thee and bring thee into trouble, and pain, and misery unutterable. Take heed of your heart, Christian; and when thou findest sorrow, trouble, and care, look within and say, “Verily, I may well receive this, considering the evil heart of unbelief which I carry about with me.”

Now dost thou see, brother Christian? No hope to escape trouble is there. What shall we do then? There is no chance for us. We must bear suffering and affliction; therefore, let us endure it cheerfully…for aught we care, the world may go on, the devil may revile, flesh may rise; “for we are more than conquerors through Him that hath loved us.” Therefore, all honor be unto God alone. ~ C.H. Spurgeon

http://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0013.cfm