Christless men may have sin dying in them, as to the outward exercise of it. Men’s bodies may be disabled for the service of their lusts, or the practice of them may not consist with their interest. Sin is never more alive than when it is thus dying. But there is a dying of it as to the root, the principle of it,—the daily decaying of the strength, power, and life of it; and this is to be had alone in Christ. Sin is a thing that of itself is not apt to die or to decay, but to get ground, and strength, and life, in the subject wherein it is, to eternity; prevent all its actual eruptions, yet its original enmity against God will still grow. In believers it is still dying and decaying, until it be utterly abolished.
– John Owen –