Hebrews 11:5-6:
By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God. But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.
Man escapes from the penalty of eternal death to eternal life only by faith in God's atonement for sin, and that atonement is in the person of the Lord Jesus Christ, who died in the sinner's place. Cain and Abel both offered a sacrifice for sin. The difference between their sacrifices was that Abel offered up a lamb, a symbol of his faith in the atonement that God would provide for his sins in the person of God's Son. Cain's sacrifice was a symbol of Cain's determination to do something in his own strength. Both believed in the existence of God and both believed they needed redemption from sin. They simply went about it in different ways. Abel who went by the way of faith, was saved, but Cain, who went by the way of his own works, was lost.