Sin is a law or a spirit that can exist at a place. Paul spoke of a law of sin at work in the members of his body. Paul exclaimed that in his mind he was in slavery to God but in his flesh he was in slavery to the law of sin. Since the chemical constituents of the physical body are morally neutral, sin must be regarded as something foreign that can be removed.
The Lamb of God has come in order to take away the sin of the world. He does this by forgiving the guilt, then giving the believer the ability to subdue it, and finally by removing its very presence.