Genesis 9:6 - Ellicott's Commentary On The Whole Bible

By man... — This penalty of life for life is not to be left to natural law, but man himself, in such a manner and under such safeguards as the civil law in each country shall order, is to execute the Divine command. And thus protected from violence, both of man and beast, and with all such terrible crimes for bidden as had polluted Adam’s beginning, Noah in peace and security is to commence afresh man’s great work upon earth.