Having addresses three big principles (that all Christians must mortify sin, that mortification is only accomplished by the Spirit, and of mortification’s usefulness), Owen now moves into his “principal intention,” which is to show how Christians should mortify our sin (53). In order to show this, he explains that the remainder of the book will consist of three parts: first, he will show what mortification of sin is (and is not); second, he will give two general directions for mortifying sin; third, he will give particular directions for the duty (54). This chapter and the following are devoted to answering the first point: what mortification is and is not, and Owen begins here by helpfully presenting false notions of mortification.
The chapter is structured simply into five examples of what mortification is not.
First, mortifying sin does not mean utterly killing it, even though we should absolutely strive to do so. He notes that:
though doubtless there may be attained, by the Spirit and grace of Christ, a wonderful success and eminency of victory against any sin, so that man may have almost constant triumph over it; yet an utter killing and destruction of it, that it should not be, is not in this life to be expected.54
He then uses Paul as an example, who freely admitted in Philippians 3:12 that he had not reached perfection against sin and would not do so until his earthly body was transformed by Christ’s mighty power (v. 21). This is a crucial point to remember because it sets us with the proper expectation in our war against sin. It calls us not to despair whenever a long-fought sin raises its wounded head yet again, and it also warns us against falling into a false sense of security over a sin that we thought we had killed.
What are the dangers of expecting complete and total mortification of sin in this life?
Second, mortification is not the hiding of outward sins. Owen’s point here is so short that it is worth quoting entirely:
When a man, on some outward respects, forsakes the practice of any sin, men perhaps my look on him as a changed man; God knows that to his former iniquity he hath added cursed hypocrisy, and is got into a safer path to hell than he was in before. He hath got another heart than he had, that is more cunning: not a new heart, that is more holy.55
Why does the replacement of outward sins for hypocrisy only create “a safer path to hell”?
Third, mortification is not the calming and quieting of passions and affections. He writes,
One man, perhaps, is never so much troubled all his life with anger and passion, nor doth trouble others, as another is almost every day; and yet the latter may have done more to the mortification of the sin than the former.55
We must take great care before passing judgment upon both ourselves and upon others. We must not think that we are truly mortifying sin simply because we are not naturally inclined to fits of anger. Nor should we immediately assume that someone who is still actively wrestling against their sinful passions is not mortifying their sin.
How do different personalities and temperaments impact our assessment of mortification?
Fourth, diverting sin is not mortifying sin. Owen cites Simon the Magician who believed the gospel and was baptized yet continued to be greedy for power whenever people receiving the Holy Spirit as the apostles laid hands upon them. Although he gave up magic, his heart remained unchanged, so he treated the indwelling of the Spirit as just another spell of magic.
He that changes pride for worldliness, sensuality for pharisaism, vanity in himself to the contempt of others: let him not think he hath mortified the sin that he seems to have left. He hath changed his master, but is a servant still.56
C. S. Lewis makes a similar point to this, although focused particularly upon how others sins are often diverted into the sin of pride:
Many a man has overcome cowardice, or lust, or ill-temper, by learning to think that they are beneath his dignity—that is, by Pride. The devil laughs. He is perfectly content to see you becoming chaste and brave and self-controlled provided, all the time, he is setting up in you the Dictatorship of Pride—just as he would be quite content to see your chilblains cured if he was allowed, in return, to give you cancer. For Pride is spiritual cancer: it eats up the very possibility of love, or contentment, or even common sense.
What is an example of such diverted sins in your life?
Fifth and finally, “occasional conquests of sin do not amount to mortifying it” (57). He then gives two occasions or seasons where sin may appear to be mortified for a time. The first is when a man is awakened suddenly “to the disturbance of his peace, terror of his conscience, dread of scandal and evident provocation of God” (57). In other words, the dreadful reality of sin is seen along with its immediate and eternal consequences, and although sin seems to be killed for a moment or two, the guilt and fear eventually die away, which emboldens sin to come out from hiding. The second is during “a time of some judgment, calamity or pressing affliction” that convicts men of their sin and leads to a momentary renouncement of sin. He cites Psalm 78:32-38 as an example of this.
Why are occasional conquests of sin not true mortification?
Let us consider carefully each of these false imitations of mortification and strive to rightly mortify our sin, as Owen will describe in the next chapter.
 C. S. Lewis, Mere Christianity, 125.
Note: page numbers are for this edition of the book.