But how is it possible that a believer, having sin in him–sin of such intense vitality, and such terrible power as we know the flesh to have–that a believer having sin should yet not be doing sin? The answer is: “In Him is no sin. He that abideth in Him sinneth not.” When the abiding in Christ becomes close and unbroken, so that the soul lives from moment to moment in the perfect union with the Lord its keeper, He does, indeed, keep down the power of the old nature, so that it does not regain dominion over the soul. We have seen that there are degrees in the abiding. With most Christians the abiding is so feeble and intermittent, that sin continually obtains the ascendency, and brings the soul into subjection. The divine promise given to faith is: “Sin shall not have dominion over you.” But with the promise is the command: “Let not sin reign in your mortal body.” The believer who claims the promise in full faith has the power to obey the command, and sin is kept from asserting its supremacy. Ignorance of the promise, or unbelief, or unwatchfulness, opens the door for sin to reign.
– Andrew Murray –