In the first chapter of Mortification of Sin in Believers, John Owen shows us how to properly view cause and effect in relation to our work of mortifying sin to the ends of which is life. It is the work of God to bring us into eternal life through Jesus Christ which is the free promise. The means by which God ordains the attainment of these ends, are subordinate to the ends prescribed.
Now, the connection and coherence of things being manifold, as of cause and effect, of way and means and the end, this between mortification and life is not of cause and effect properly and strictly, —for “eternal life is the gift of God through Jesus Christ,” Rom. vi.23,—but of means and end. God hath appointed this means for the attaining that end, which he hath freely promised. Means, though necessary, have a fair subordination to an end of free promise. A gift, and procuring cause in him to whom it is given, are inconsistent. The intendment, then, of this proposition as conditional is, that there is a certain infallible connection and coherence between true mortification and eternal life: if you use this means, you shall obtain that end; if you do mortify, you shall live. And herein lies the main motive unto and enforcement of the duty prescribed.