Christians are constantly engaged in active battle:
For the flesh sets its desire against the Spirit, and the Spirit against the flesh; for these are in opposition to one another… (Gal. 5:17)
At any moment, ground is being won. We are either aligned with the Spirit and overcoming temptation or giving ourselves over to the enemy. My track coach used to tell us as athletes, “Every day you are either getting better or worse as a runner. There is no such thing as staying the same.” C.S. Lewis may have said it better as it pertains to our spiritual lives, “There is no neutral ground in the universe: every square inch, every split second, is claimed by God and counterclaimed by Satan.”
Think of how unfair it is when we choose to put things before our eyes (literally and figuratively) that aid the enemy in battle. When we do this we are putting weapons in the hand of Satan, while de-arming the Spirit. John Owen illustrates this in spiritual battle:
Now this is, first, the most unjust and unreasonable thing in the world, when two combatants are engaged, to bind one and keep him up from doing his utmost and to leave the other at liberty to wound him at his pleasure; and, secondly, the most foolish thing in the world to bind him who fights for our eternal condition and to let him alone who seeks and violently attempts our everlasting ruin. THE CONTEST IS FOR OUR LIVES AND SOULS.
This is unjust and unreasonable. Imagine what this would look like on the beaches of Normandy – soldiers being forced into the fire of enemy soldiers while they march uphill empty handed. WE MUST FIGHT! Or as John Piper says, “Make war with sin!” However, to do this in our own power is a great travesty. For to fight apart from the Spirit is to have “no strength in combat.” It is to fight the necessary battle, but always come up short and never conquer. Instead being a Christian soldier means actively allowing the Spirit to fight through you:
He (the Spirit) works upon our understandings, wills, consciences, and affections, agreeably to their own natures; he works in us and with us, not against us or without us; so that his assistance is an encouragement as to the facilitating of the work, and no occasion of neglect as to work itself.
How does the Spirit mortify sin?
- By causing our hearts to abound in grace and the fruits that are contrary to the flesh, and the fruits thereof and principles of them.
- By a real physical efficiency on the root and habit of sin, for the weakening, destroying, and taking it away.
- He brings the cross of Christ into the heart of a sinner by faith, and gives us communion with Christ in his death and fellowship in his sufferings.
For more: Overcoming Sin and Temptation by John Owen.