Do you have a dog at your house? Many times the family dog will wait at the door for the owner to let it inside. If the family goes away and leaves their dog outside, they often find the dog waiting at the door when they return. There is a reason for that. The dog loves the family and that is good. It is bad if sin lies at the door! Cain had it at his door.
“So the LORD said to Cain, ‘Why are you angry? And why has your countenance fallen? If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it (Genesis 4: 6-7 NKJ).” God gave Cain the opportunity to repent of evil attitudes of envy against his brother. Rejecting the warning, he plotted murder.
“Cain rose up against Abel his brother and killed him (Genesis 4:8b NKJ).” Sin knocked at Cain’s door and he invited it in. How tragic, that Cain refused to listen to God’s warning and advice to resist evil. Brother killed brother; parents grieved and Cain became an outcast. When sin waits at my door, I am in great danger and will recall God’s command to rule over it.