John Owen described in chapter 12 of Indwelling Sin in Believers how the deceit of sin progressively works towards the birth of actual sin. He said this happens by distracting the mind from its duty, then entangling the affections, which leads to the thought of sin so that it may be brought forth. “Then lust (or desire) when it has conceived gives birth to sin” (James 1:15).

In order for the conception of sin to result in the actual sin, it must have the consent of the will. Without the agreement of the will, sin cannot be committed. When the will has acquiesced to sin, there is nothing in the soul to hinder it’s actual manifestation. But God has various ways of frustrating the birth of these conceptions, causing them to fade away in the mind that first devised them.

This is so that not even the smallest part of the sin which may be willed or conceived is committed, even though there is nothing in the soul to prevent it from occurring once it has yielded. It’s like when a cloud is full of rain and ready to fall, but a wind comes and drives the cloud away. The will is ready to bring forth sin, but by one wind or another, God diverts it. This is even if the cloud was as full of rain as if the rain had already fallen; if the soul was as full of sin as if it had already been committed the sin.

The conception of lust or sin is therefore necessary to obtain the consent of the will to its enticement. The will is the primary cause of obedience and disobedience. Moral actions done to us or that are in us are good or evil to the extent they partake of the consent of the will. “Every sin is so voluntary, that if it be not voluntary, it is not sin.” This is ultimately true of actual sins. An Aristotelian sense of formal cause in the iniquity of actual sins arises from the acts of the will in them and concerning them. Owen said by this he means the people who commit sin. Otherwise, in itself, the formal reason for sin is its deviation from the law of God.

He said there is a twofold consent of the will with regard to sin. The first is seen in the full, absolute, complete consent following a deliberation by the will. The convictions of the mind are conquered and there is no principle of grace in the will to weaken it. It is as if the soul is a ship before the wind, “with all its sails displayed, without any check or stop.” It rushes into sin, like a horse charging into battle. As it says in Ephesians 4:19, “they have given themselves up to sensuality, greedy to practice every kind of impurity.”

This is that consent of the will, which is acted in the finishing and completing of sin in unregenerate persons, and is not required to the single bringing forth of sin, whereof we speak.”

Secondly, there is a consent of the will that is joined with a secret opposition to the temptation to sin and a desire to the contrary. We see this in Peter denying his master. His will was in the denial or he would not have done it. It was a voluntary action that he chose to do at that time. However, there was within Peter’s will an opposing principle of love to Christ and faith in him that did not utterly fail. “The efficacy of it was intercepted, and its operations suspended actually, through the violent urging of the temptation that he was under.” Although it was within his will, and even weakened his willingness to deny Christ, it was not done with the sense of self-pleasing that usually accompanies full, absolute, complete consent of the will.

Although there may be a predominant consent in the will, which may be sufficient for the conception of certain sins, there cannot be an absolute, total, full consent of the believer to any sin. There is in his will a principle fixed on good for all—the principle of grace. “Grace has the rule and dominion, not sin, in the will of every believer.” Consent to sin in the will, which is contrary to the inclination to do good, is not—and cannot be—total, absolute and complete. Not only is there a general prevailing principle against sin in the will, there is also a secret reluctancy to its own action in consenting to sin.

It is true that sometimes the soul is not conscious of this reluctance because the present consent of the will carries away an awareness of the principle of grace in the will. But the general rule holds true in all things and at all times: “the desires of the Spirit are against the flesh” (Galatians 5:17). This is so, though not always to the same degree, nor with the same success.  The dominance of the contrary principle, namely the desires of the flesh, in this or that particular act does not disprove it.

But this is true when the opposite is considered. “There is no acting of grace in the will, but sin lusts against it.” While that lusting may not be conscious in the soul, it is enough to keep those actions of grace from perfection. “So it is in this opposition of grace, against the acting of sin in the soul; though it be not sensible in its operations, yet it is enough to keep that act from being full and complete.” A significant amount of spiritual wisdom is needed to rightly discern between the spiritual opposition of the principle of grace in the will against sin, and the rebukes given to the soul by the conscience for the conviction of sin.

Take note that repeated acts of willful consent to sin may generate a habitual inclination towards similar acts. This may bring a tendency to the will of easily or impulsively consenting to sin, a dangerous condition to the soul that should be guarded against. This consent which has been described, may be considered in the following ways. First it becomes accustomed to the circumstances, causes, means, and inducements to sin. Then it begins to value the actual sin.

In the first sense, there is a virtual consent of the will to sin. In every laxity to the prevention of it, in every neglect of duty that makes a way for it, in every hearkening to a temptation that leads towards it. “In a word, in all the diversions of the mind from its duty, and entanglements of the affections by sin, before mentioned.” Remember that where there is no formal act of the will, there is no sin. But we were supposed to speak of the consent of the will to actual sin, so far as it is— one way or the other—either committed or prevented.

This is the way that the deceit of sin proceeds to procure the consent of the will in order to conceive actual sin. Note first that the will is a rational appetite. It is rational when guided by the mind, and an appetite when excited by the affections. Second, it only chooses that which has the appearance of good. It cannot agree to anything it sees as evil. “Good is its natural and necessary object, and therefore, whatever is proposed to it for its consent, must be proposed under an appearance of being either good in itself, or good at present to the soul.”

Our way is therefore made somewhat plain. We have seen how the mind is drawn away by the deceit of sin, and how the affections often become entangled. What remains is to discover some of the special deceits, their corrupt and fallacious reasonings, and then show how they prevail on the will to consent to sin.

The will is imposed upon by corrupt reasoning, namely that grace is exalted in pardon and mercy is provided for sinners. This first deceives the mind, which opens the way to the will’s consent by hiding the evil from it. In carnal hearts, this prevails to make them think their liberty consists in being “slaves of corruption,” forgetting that “Whatever overcome a person, to that he is enslaved” (2 Peter 2:19). This poison often taints the minds of believers themselves, which we are cautioned against in Scripture.

There is a twofold mystery of grace—of walking with God, and of coming to God. The grand design of sin is, to confuse the doctrine and mystery of grace in reference to these things. This is done by applying those considerations to the one which are properly applied to the other, so that each part is hindered; and the influence of the doctrine of grace on them is defeated. “I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous. He is the propitiation [means of forgiveness] for our sins” (1 John 2:1-2). Here the entire design and use of the gospel is briefly expressed.

There is full relief in the propitiation and intercession of Christ for us. “This is the order and method of the doctrine of the gospel, and of the application of it to our own souls: first to keep us from sin, and then to relieve us against sin.” But here enters the deceit of sin. It changes the method and order of the application of gospel truths. It takes up the last first, namely to relieve us of sin. And this excludes the use of the first utterly! If any man sin, there is pardon provided. This is all that the gospel would willingly have us remember.

“The grace of God brings salvation, having appeared unto us to that end and purpose.” When we should come to God by believing, the deceit of sin emphasizes keeping free from sin, where the gospel proposes there is pardon from sin for our encouragement. When we should come to God and walk with him, the deceit of sin points to there being pardon for sin, where the gospel primarily proposes we should keep ourselves from sin.

Now the mind, when it is entangled by this deceit and diverted from the true end of the gospel, tries several tactics upon the will to obtain its consent. First, it launches a sudden surprise in the midst of temptation. When a temptation befalls the soul, the principle of grace in the will rises up with a rejection of it. But suddenly, the mind, “being deceived by sin, breaks in upon the will, with a corrupt, fallacious reasoning from gospel grace and mercy.” Then it halts the will’s opposition and tips the scale to the side of temptation by presenting evil as a present good. Thus, sin is conceived in the sight of God, although it may never be committed.

It also gains the will’s consent unconsciously. It insinuates the poison of this corrupt reasoning little by little, until it has greatly prevailed. The entire apostasy from the gospel is principally the casting of the soul into the mold of this false reasoning, so that sin may be indulged in because of grace and pardon. “Hereby is the soul gratified in sloth and negligence, and taken off from its care as to particular duties, and avoidance of particular sins.” It transfers the works of the soul from the mystery of the law of grace to searching for salvation as if we had never performed any duty.

This is the common way of sin’s procedure in the destruction of souls, which seem to have made some good engagements in the ways of God. When it hath entangled them with one temptation, and brought the will to some liking of it, that presently becomes another temptation, either to the neglect of some duty, or to the refusal of more light; and commonly, that whereby men fall off utterly from God, is not that wherewith they are first entangled.