In this chapter Owen argues that the mortification of sin is the means through which God often works in order to promote spiritual stregth and peace. The good doctor is careful to say that mortification is not the source of our spiritual life or comfort, for this comes directly by God's sovereign work of regeneration. However, though we are passed from death to life in regeration, our own experience of that life is very much dependendant on our personal practice of mortificaiton.
I thought Owen's analogy of a plant was particularly helpful in elucidating this point:
Now, as you may see in a garden, let there be a precious herb planted, and let the ground be untilled, and weeds grow about it, perhaps it will live still, but be a poor, withering, unuseful thing. You must look and search for it, and sometimes can scarce find it; and when you do, you can scarce know it, whether it be the plant you look for or not; and suppose it be, you can make no use of it at all. When let another of the same kind be set in the gound, naturally as barren and bad as the other, but let it be well weeded, and everything that is noxious and hurtful removed from it- it flourishes and thrives; you may see it at first look into the garden, and have it for you used when you please. So it is with the graces of the Spirit that are planted in our hearts. That is true . . .they abide in a heart where there is some neglect of mortification; but they are ready to die, they are withering and decaying. . . Such a man may search for faith, love, and zeal, and scarce be able to find any; and if he does discover that these graces are there yet alive and sincere, yet they are so weak, so clogged with lusts, that they are of very little use . . . But now let the heart be cleansed by mortification, the weeds of lust constantly and daily rooted up . . . let room be made for grace to thrive and floursih - how will every grace act its part, and be ready for every use and purpose. (Owen, Overcoming Sin and Temptation, 66)
Does this illustration ring true with you? How have you seen the Spirit's fruit in your heart wither when you have not fought against sin and flourish when you are activly mortifying the lusts of the flesh?