Then the LORD said to Cain, “Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.” (Gen 4:6-7)
The experience of temptation outside the Garden of Eden is described first as an internal battle, where Cain must address his own (fallen) nature in order to live God’s way. There is no snake opposing him, seeking his undoing. He must address himself. Sin desires to rule him, but he must rule over it.
Sin is an opportunistic foe. It waits, crouching, coiled for action at a moment’s notice. God unmasks sin for Cain’s benefit. He must know his enemy and how sin plots his demise. But Cain refuses the warning. Instead he invites Abel to ‘come for a walk’. It sounds innocent enough. But his evil intent is soon revealed.
Cain’s own sinful nature pounced upon him, unbridled and indulged. Cain then pounced upon Abel.
In his fallen state Cain is told what to do with sin— he must rule over it. I don’t suppose God would not ask him to do the impossible. And so, in our state (fallen, but with the Spirit) we must also rule over our sin. As Christians, enabled by God’s Spirit, we talk back to our urge to sin, we address pride, greed and lust. We say ‘No’. Instead, we look for the alternate path, the way out, God’s provision of grace.
So, if you think you are standing firm, be careful that you don’t fall! No temptation has overtaken you except what is common to mankind. And God is faithful; he will not let you be tempted beyond what you can bear. But when you are tempted, he will also provide a way out so that you can endure it. (1 Cor 10:12-13)