Jamieson, Fausset and Brown on Romans 6:12

12. Let not sin therefore--as a Master

reign--(The reader will observe that wherever in this section the words "Sin," "Obedience," "Righteousness," "Uncleanness," "Iniquity," are figuratively used, to represent a Master, they are here printed in capitals, to make this manifest to the eye, and so save explanation).

in your mortal body, that ye should obey it--sin.

in the lusts thereof--"the lusts of the body," as the Greek makes evident. (The other reading, perhaps the true one, "that ye should obey the lusts thereof," comes to the same thing). The "body" is here viewed as the instrument by which all the sins of the heart become facts of the outward life, and as itself the seat of the lower appetites; and it is called "our mortal body," probably to remind us how unsuitable is this reign of sin in those who are "alive from the dead." But the reign here meant is the unchecked dominion of sin within us. Its outward acts are next referred to.