Charnock first introduces his text, Romans 8:13, “For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live.” He makes the point that, “You must not imagine you shall be justified without being sanctified.” There is a strange belief that (using an image from Dallas Willard) salvation is sort of like an arbitrary barcode slapped onto a product. The scanner reads the code and ignores the item. If a “soap” barcode is put on a box of cereal, the scanner reads “soap.” We believe that if we receive the barcode “saved” that will read by the scanner on judgment day, no matter who we are.

Charnock then defines “flesh” and “body”: “Some, by flesh, understand the state under the law; others, more properly, corrupted nature. Ye shall die, without hopes of a better life. But if you mortify the deeds of the body: the deeds of the body of sin, which is elsewhere called the body of death; the first motions to sin and passionate compliances with sin, which are the springs of corrupt actions. Corrupt nature is called a body here, morally, not physically; it consisting of divers vices, as a body of divers members.”

The verse consists of a threat and a promise; an act and an object. A great deal of Puritan precision is simply a matter of paying attention to the text. Exegesis is a matter of paying attention, asking questions and thinking. When people first hear someone carefully exegete a text is sounds like magic; when in fact it is merely carefully reading.

Charnock then makes a few deductions from the text. “Sin is active in the soul of an unregenerate man.” Second, “Nothing but the death of sin must content a renewed soul. The sentence is irreversible: die it must.” This is a present tense, continual action. 

“The knife must still stick in the throat of sin, till it fall down perfectly dead. Sin must be kept down though it will rage the more, as a beast with the pangs of death is more desperate.”

This rampage against sin must be universal, from all actions and intentions, from the first motion to the last completion.

“The greatest object of our revenge is within us. Our enemies are those of our own house, inbred, domestic adversaries; our anger is then a sanctified anger when set against our own sins. Our enemy has got possession of our souls, which makes the work more difficult.”

How then is this done?  “Man must be an agent in this work. We have brought this rebel into our souls, and God would have us make as it were some recompence by endeavouring to cast it out; as in the law, the father was to fling the first stone against a blasphemous son.”

And how, “Through the Spirit. (1.) Mortification is not the work of nature; it is a spiritual work. Every man ought to be an agent in it, yet not by his own strength.” 

And here a bit of summary, “The difficulty of this work is hereby declared. The difficulty is manifested by the necessity of the Spirit’s efficacy. Not all the powers on earth, nor the strength of ordinances, can do it; omnipotency must have the main share in the work.”

And from this the “doctrine”, the thesis statement: 

The doctrine to be hence insisted on is this: Mortification of sin is an universal duty, and the work of the Spirit in the soul of a believer, without which there can be no well-grounded expectations of eternal life and happiness.