If thou dost well, shalt thou not be accepted? — Either, 1. If thou hadst done well, as thy brother did, thou shouldest have been accepted as he was. God is no respecter of persons; so that if we come short of acceptance with him, the fault is wholly our own. This will justify God in the destruction of sinners, and will aggravate their ruin. There is not a damned sinner in hell, but if he had done well, as he might have done, had been a glorified saint in heaven. Every mouth will shortly be stopt with this. Or, 2. If now thou do well: if thou repent of thy sin, reform thy heart and life, and bring thy sacrifice in a better manner; thou shalt yet be accepted. See how early the gospel was preached, and the benefit of it here offered even to one of the chief of sinners.
He sets before him death and a curse; but, if not well — Seeing thou didst not do well, not offer in faith, and in a right manner, sin lieth at the door — That is, sin only hinders thy acceptance. All this considered, Cain had no reason to he angry with his brother, but at himself only. Unto thee shall be his desire — He shall continue in respect to thee as an elder brother, and thou, as the first — born, shall rule over him as much as ever. God's acceptance of Abel's offering did not transfer the birth — right to him, (which Cain was jealous of) nor put upon him that dignity, and power, which is said to belong to it, Genesis 49:3.