‘Yahweh said to Cain, ‘why are you angry, and why does your face express such disapproval? If you do well, is there not a lifting up? And if you do not do well, sin is couching at the door. It longs to grab you, but you must overcome it.'
We do not know how God communicated with Cain. Possibly it was in his heart. But Cain well knew, as we so often do when we would rather not, what God was trying to tell him. His problem lay in not ‘doing well'. There was something wrong with his attitude and behaviour, and he knew it. Note how ‘doing well' is compared with the value of worship in Isaiah 1:17 and Jeremiah 7:5. If a man does not ‘do well' his sacrifice is unacceptable.
The phrase ‘is there not a lifting up' is translated ‘will you not be accepted' in RSV and NIV, understanding it as meaning a lifting up of the face and therefore an acceptance, but the verb when not qualified by other words usually means a lifting up of the spirits, and therefore probably here means ‘will you not feel good?' Cain's very failure to feel good was, as God reminds him, because of his own behaviour. Thus he is promised that joy will return with obedience. Either way the assumption is the same in the end, the consciousness of being accepted.
Perhaps it was because he had not worked diligently that the produce had dwindled. Or possibly there was something else. But if he would but behave rightly, then his offering would be accepted, and he would prosper. But if he continued as he was, then sin, which sat couching outside his tent like a wild animal waiting for its prey (a vivid picture), would seize him and carry him off.
Right from the start then we learn that ‘to obey is better than sacrifice' (1 Samuel 15:22 compare Isaiah 66:3). But Cain let his grievance fester in his heart until finally he came to his ultimate decision, and allowed sin to ‘carry him off'. What an important lesson there is here for us. If we allow a grievance to fester in our hearts, who knows what it can lead to?