Matthew Poole and continuators on Genesis 4:15

15. And the LORD said unto him, therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold . And the LORD set a mark upon Cain , lest any finding him should kill him.

Or, Assuredly, as the word signifies Ier. 2. 32. and 5. 2. Zach. 11. 17. That thou mayst see how I hate murther, and how impartially I shall punish all Murtherers, and that thou mayst be unhappily free from this fear, that thou mayst live for an example to mankind, for a terrour to thy self and others.

(i. e.) Abundantly he shall be plagued with many and grievous punishments, as the phrase is used, Levit. 26. 28. Psal. 12. 7. and 79. 12. and in many other places.

What this was, whether a trembling of his Body, or a ghastliness of his countenance, or what other visible token of the divine displeasure, God hath not revealed, nor doth it concern us to know.