Hebrews 4:12-13 tells us, "For the word of God is living and active and sharper than any two edged sword, piercing as far as the division of soul and spirit, of both joints and marrow, and able to judge the thoughts and intentions of the heart."
Look at the image of the sword. If the blade were sharp only on one side, it's use would be limited.This is a formidable weapon no matter what direction you swing it. God's word is just such a weapon. But instead of dealing death, it deals LIFE!
Sin whispers through the desires of the flesh and the rationalizations of the mind. "You won't have a chance in the future if you don't cheat on this test." "You won't be noticed if you don't dress this way." "You won't have job security if you speak up about dishonest practices at work." "Your life will be wasted in this relationship, you should just get a divorce." "Only a fool would go around looking weak instead of getting revenge." These are all lies...every one of them.
It is the deceitfulness of sin made manifest in the flesh. These lies and others can lodge themselves very deep in our hearts. They will stay in our minds as thought and intentions. They will seem unshakably true because of the hardness of the heart that encloses them like a dark, sealed casket.
When the heart and the mind are in this condition, unbelief has the upper hand. They block out the teachings that we know are true. Instead of trusting in the promises of God, we are believing in the promises of sin.
The Word of God is living, active and sharp. It will penetrate deeper than the deception of sin has ever gone and reveal what is truly worth trusting.