Enmity exerts itself is opposition. Enmity will oppose and contend with what it is at enmity with. Things natural and moral work this way also: as light and darkness, heat and cold oppose each other, so do virtue and vice. So is it with sin and grace. The apostle says, "These are contrary the one to the other" (Gal 5:17)—that is, they are placed and set in mutual opposition, and that continually and constantly, as we shall see.