Gen. 4.7 And if you do not do well, sin is crouching at the door. Its desire is contrary to you, but you must rule over it.
Sin wants us. Sin is crouching at the door desiring to destroy us.
Is this simple exaggeration, the personification of an inanimate thing, sin? No! Think about it. Sin as a concept is inanimate, the transgression of the law of God. Usually we would say that a transgression, a breaking of the law, cannot be said to desire something.
But sin never has its origin in an inanimate object. Where does sin come from? The devil, the evil world system, and our own sin nature, the flesh.
Certainly the devil is crouching at our door, seeking to devour us with sin, tempting and enticing. He desire our destruction. "The thief comes only to steal and kill and destroy" (John 10:10a). He is a roaring lion seeking to devour us! "Your adversary the devil prowls around like a roaring lion, seeking someone to devour" (1 Peter 5:8). There is nothing passive about the devil, sin, and his desire for us!
So, too, the world system of evil is not neutral toward people, or believers. It has a desire, too, to consume and conform us. This desire is expressed in the will, not of things per se, but in the collective will of sinful humanity. "For all that is in the world—the desires of the flesh and the desires of the eyes and pride of life—is not from the Father but is from the world" (1 John 2:16). The world now commands us all, for example: "Question your gender or die!" The world is not neutral in its evaluation of Christians, it positively hates us and works for our destruction. "Do not be surprised, brothers, that the world hates you" (1 John 3:13).
Even our own sin is rightly seen as a restless evil desire. "But each person is tempted when he is lured and enticed by his own desire" (James 1:14). Our sin nature has a desire for us, too, to entice us to destruction. If we live by it, according to its desire for us--as did Cain--it will lead to our destruction. "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" (Romans 8:13). We dare not assume the neutrality of the sin in our own hearts, but see that this sin has an intention as well.
What do we do to face this enemy? You must rule over it! We are, by the grace of God the Father, the power of Christ's resurrection, and the presence of the Holy Spirit, to fight against sin, driving it from our door, not yielding to its Siren song, but putting it to death by the power of the Spirit. (Romans 8.13)
What we must never miss is this warning of God to Cain, and through Cain to us. "Sin is crouching at the door. Its desire is contrary to you, but you must rule over it." We must fight it where ever we find it, subdue it, kill it, rule over it, and never make peace with sin. As John Owen rightly said, "Be killing sin or it will be killing you."