When Cain fought with Able, did he understand the concept of killing and murder? If not, would he be guility of first degree (or possibly second degree) murder ? Why did the Lord protect Cain? What was the purpose the "mark" . In Judaism, the mark is not a punishment but a sign of God's mercy. When Cain was sentenced to be a wanderer he did not dispute the punishment but only begged that the terms of his sentence be altered slightly. According to The Midrash and the Conflict of Adam and Eve with Satan both record that the real motive involved the desire of women. According to Midrashic tradition, Cain and Abel each had twin sisters, whom they were to marry. The Midrash records that Abel's promised wife was the more beautiful. Cain would not consent to this arrangement. Adam proposed to refer the question to God by means of a sacrifice. God rejected Cain's sacrifice, signifying His disapproval of his marriage with Aclima, and Cain slew his brother in a fit of jealousy. From Wikipedia Is it possible that Cain did reprent of his sin.