The Bible consistently teaches us that we must be killing sin. Different language is used in different places, but the point is always the same. In Matthew 18:7-9, Jesus teaches this in conjunction with a warning about hell.

“Woe to the world for temptations to sin! For it is necessary that temptations come, but woe to the one by whom the temptation comes! And if your hand or your foot causes you to sin, cut it off and throw it away. It is better for you to enter life crippled or lame than with two hands or two feet to be thrown into the eternal fire. And if your eye causes you to sin, tear it out and throw it away. It is better for you to enter life with one eye than with two eyes to be thrown into the hell of fire.”

This shows us something about the relationship between sin and eternal damnation. Note that this is not focusing on the “legal dimension” of that relationship. Matthew 18:7-9 is not about justification. There is nothing at all in Jesus’ warning here that conflicts with the truth that we are made right with God entirely by the blood and righteousness of Christ received by faith alone (cf. Rom. 3:24-28). Our passage here is about the moral or experiential dimension of this relationship. 

The Puritan John Owen famously wrote on the subjects that are at the heart of this teaching. I will enlist his help here especially on the mortification of sin, which is really what Jesus is driving at in the extreme imagery of cutting off the hand or foot, or tearing out the eye. 

What is Meant by the Mortification of Sin?

The text that Owen launched off from is Romans 8:13 where Paul says, “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.” Owen exposits this verse in five points: namely, 1. its duty to mortification, 2. believers as its subject, 3. the promise of eternal life attached, 4. the Holy Spirit as the principle (or efficient) cause, and 5. the conditionality element.1

It is that last point which immediately distracts many Christians from taking in the lesson. Even granting that there is conditionality in a gracious covenant, Owen is clear that the cause-effect relationship “between mortification and life is not of cause and effect properly and strictly,” since eternal life is a gift of God most immediately through faith alone. Hence, “God hath appointed this means for the attaining that end, which he hath freely promised.”2 As to this being a duty, Owen points to the obvious about killing: take away the life of any thing, and all its principle to act is also removed.  “Indwelling sin is compared to a person, a living person, called ‘the old man.’3 

And then he sets forth his famous maxim,

“Do you mortify; do you make it your daily work; be always at it whilst you live; cease not a day from this work; be killing sin or it will be killing you.”4

What does he mean by this? He says, “He that stands still and suffers his enemies to double blows upon him without resistance, will undoubtedly be conquered in the issue … There is not a day but sin foils or is foiled, prevails or is prevailed on; and it will be so whilst we live in this world.”5 Every unmortified sin, according to Owen, will do two things to the soul. It will weaken it and darken it. He argues from Romans 7:23, Galatians 5:17, and James 1:14 and 4:5, that the battle between spirit and flesh always rages, and thus implies of indwelling sin, “in every moral action it is always either inclining to evil, or hindering from that which is good, or disframing the spirit from communion with God.”6 

Some Further Distinctions on Sin-Killing

Owen lists five things that mortification is not:

First, “To mortify a sin is not utterly to kill, to root it out, and destroy it, that it should have no more hold at all nor residence in our hearts. It is true that this is what we aim at; but this is not in this life to be accomplished.” Second, mortification is not the mere “dissimulation of a sin,” or that man who merely conceals. Such a man, Owen says, has only another heart such as “he had, that is more cunning; not a new heart, that is more holy.” Third, “mortification of sin consists not in the improvement of a quiet, sedate nature.” Burroughs had said much the same about a heart outwardly quiet not necessarily being contentment, but rather natural passivity and indifference. Fourth, a “sin is not mortified when it is only diverted.” The example of Simon Magus is cited here, who was prepared to leave his sorceries but not his “covetousness and ambition.” Fifth, “occasional conquests,” or that only for a season, is not the mortification of sin. Though the man may awake all that is in him, like a general summoning all his guards to make inquiry in the whole camp, yet the enemy of sin “until the noise and tumult be over, hides himself, or lies like one who is dead, yet with firm resolution to do the like mischief again upon the like opportunity.”7 

Owen argues on the one hand that one cannot uproot indwelling sin in this life, and yet he insists that we must strike upon the root and not its fruit. The resolution of the paradox is not hard. It is the weakening of the sin that is affected by the root-work, that is, at the level of the “old man” or “body of sin,” or its allure to the heart. And while there is no complete eradication (victory) over sin this lifetime, yet one has not mortified unless there is “pursuit of it to a complete conquest.”9 But the distinction to make is between indwelling sin, its nature and principle, versus particular sins, its activities and domineering power. Think of the difference as that between a war and a battle. 

I will add one last point on those opening words of Jesus. The imagery of Matthew 18:7-9 is hyperbole—the seriousness is not. In other words, the comparison itself is not hyperbole. If it really is “better” to lack these instruments of the body, well, then it is no exageration at all to make the comparison. What is hyperbolic is the imperative dimension. These things—the hands, the feet, and the eyes—are not really the root of sin, so that to root them out would not actually be to root sin out anyway. But Jesus warms us up to the real fight with imagery that we can understand. The value of the violent imagery is in the urgency of the warfare.

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1. John Owen, The Mortification of Sin from The Works of John Owen, Volume VI (Edinburgh: Banner of Truth, 1981), 5-6.

2. Owen, The Mortification of Sin, 6.

3. Owen, The Mortification of Sin, 8.

4. Owen, The Mortification of Sin, 9.

5. Owen, The Mortification of Sin, 11.

6. Owen, The Mortification of Sin, 11.

7. Owen, The Mortification of Sin, 24-26.

8. Owen, The Mortification of Sin, 32.