Owen's book is primarily an exposition and application of Romans 8:12-13: "So then, brothers, we are debtors, not to the flesh, to live according to the flesh. For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live." Just what does the promise "you will live" involve? One way of getting at the answer is to go back up to verse 6: "To set the mind on the flesh is death, but to set the mind on the Spirit is life and peace." To live is to experience "life and peace." I take this to mean both eternal life and the objective peace with God that accompanies eternal life, as well as the more subjective experience and enjoyment of life and peace as we walk with Christ now. I think Owen would agree with this - at least the content of chapter four seems to lead in that direction, as Owen explores "how life and comfort depend on mortification." "As we walk with our God we desire greatly His strength, comfort, power and peace," writes Owen. "The realization of these, and thus the joy of our spiritual life, depends greatly upon the mortification of sin" (p. 21).Then follows a couple of clarifications.
1. Owen does not say that they (strength, comfort, power, peace, and joy) proceed from it, as though they were necessarily tied to it. In fact, Owen believes that "a man may be carried on in a constant course of mortification all his days, and yet perhaps never enjoy a good day of peace and consolation" (p. 21). He references Psalm 88 in defense of this. I'm not sure that I agree with Owen on this point, though. It is hard for me to believe that a new covenant believer could live in the regular practice of mortification and still not enjoy some measure of comfort and joy in walking with the Lord, Psalm 88 notwithstanding. We do need to remember that the psalms have an occasional nature about them, being written as they were in specific sets of circumstances by specific people. It is unlikely that Psalm 88 was (or is) the constant, unending experience of anyone. However, I do think Owen is right when he says "The use of means for the obtaining of peace is ours; the bestowing of it is God's prerogative" (p. 22). In other words, there is a real work of God in giving peace to the soul that is above and beyond that which we can produce in ourselves by the use of means.
2. Following the first clarification, Owen says that "mortification is not the immediate means that God has instituted to give us life, vigour, courage, and consolation. The immediate cause of these privileges is our adoption" (p. 22). See Rom. 8:16.
3. BUT, Owen does say (and this is not a contradiction, it just shows how nuanced Puritan logic can be) "In our ordinary walking with God, and in the ordinary course of his dealing with us, the vigour and comfort of our spiritual lives depend much on our mortification. Mortification not only bears a cause-and-effect relationship to our joy, but it works effectually to bring it to pass" (p. 22).Why is this so? Because "mortification prevents sin from depriving us of health in our spiritual life" (p. 22). Unmortified sin does two things to rob us of joy and spiritual health.
(1) Unmortified sin weakens the soul, because sin "untunes and unframes the heart itself, by entangling its affections" (p. 23), "sin fills the thoughts with its enticements" (p. 23), and "sin breaks out and actually hinders duty" (p. 23).
(2) Unmortified sin darkens the soul. "It is a cloud, a thick cloud, that spreads itself over the face of the soul, and intercepts all the beams of God's love and favour. It takes away all sense of the privilege of our adoption; and if the soul begins to gather up thoughts and consolation, sin quickly scatters them" (p. 24).Owen then gives an analogy that is quite helpful. He compares the mortification of sin in our hearts to the weeding of a garden. If a garden is left to itself, it will be overgrown with weeds and the good plants will be choked out by the weeds. So a person who doesn't attend to mortifying sin will find his heart overgrown with sin, so that the comfort and joy of walking with Christ choked out by the sin. On the flip side, there is more to growing a healthy garden than weeding it. Good seeds must be planted, watered, and fertilized - and then God must given the growth.