Genesis 9:5 - Wesley's Explanatory Notes

And surely your blood of your lives will I require — Our own lives are not so our own, that we may quit them at our own pleasure; but they are God's, and we must resign them at his pleasure. If we any way hasten our own deaths, we are accountable to God for it. Yea, At the hand of every beast will I require it — To shew how tender God was of the life of man, he will have the beast put to death that kills a man. This was confirmed by the law of Moses, Exodus 21:28, and it would not be unsafe to observe it still. And at the hand of every man's brother will I require the life of a man — I will avenge the blood of the murdered upon the murderer. When God requires the life of a man at the hand of him that took it away unjustly, he cannot render that, and therefore must render his own in lieu of it, which is the only way left of making restitution.