George Leo Haydock

Shed. God had not subjected Cain to this law of retaliation, as he was the first murderer, and the earth was unpeopled. (Haydock) — Here he declares, that it is just to inflict such a punishment on the offender. (Menochius) — Judges are hence authorized to punish murderers with death. (Calmet) — The general law, thou shalt not kill, admits of exceptions, and forbids killing by private authority, or out of revenge. (Haydock) — The blood of your lives, may signify the blood on which your life depends; or, according to the Rabbin, it is a prohibition of suicide, which one would think is so contrary to the first law of nature, self-preservation, as to require no prohibition; and yet, to the scandal of philosophers, some have written in its defence! (Haydock)