“Mortification is the soul’s vigorous opposition to self” – so says John Owen in his Mortification of Sin. Mortification is our work & the Spirit’s work in killing sin; in fighting sin. Sin will not go away & will not leave us alone. It is like the weeds of the ground; if you do not tend your garden & its flowers, the weeds will come & destroy all that you have worked for.
Thus sin can destroy joy in a moment. It can reduce faith to apprehension in the stroke of a heartbeat. So we must labor hard at weeding out sin & its remaining strength. We are in a spiritual war. This war is in the good providence of God & is designed to wean us from all worldly attachments & allurements. Providence is that means of God by which he reveals to us the hidden power of our corruption, the wickedness of our hearts, so that we might be humbled.
Why does God do this? He does this, so that we might cast ourselves upon him with no strength of ourselves retained. God drives us to seek him by reducing us. All this activity of God is providential & gives God the glory & brings good to us. So we must wage war against sin. it will not lie down & go away – but providence is working.