Genesis 9 · a question people ask
In 9:6, is "his blood will be shed by man" a command or a warning?
"Whoever sheds man’s blood, his blood will be shed by man, for God made man in his own image." The Hebrew verb can be read as "will be shed" (what will happen) or as a command, that it is to be shed (what must be done). Protestants read it both ways. All agree on the reason the verse gives: "God made man in his own image."
How Christians read it
Where Christians differ, Favor sets out the main views side by side and doesn't pick one.
A command to people
God has just said he will require an accounting "at the hand of man" (9:5), and here people are the ones who carry it out. The law later says no atonement can be made for the land for blood shed in it "but by the blood of him who shed it" (Numbers 35:33), and Paul says the governing authority "doesn’t bear the sword in vain" (Romans 13:4).
Genesis 9:5-6 · Numbers 35:33 · Romans 13:4
A warning of what comes back
The verse describes how violence returns on the violent, as Jesus says: "all those who take the sword will die by the sword" (Matthew 26:52). On this reading it states the weight of murder without itself setting out who must act.
Genesis 9:6 · Matthew 26:52
The verses
“Whoever sheds man’s blood, his blood will be shed by man, for God made man in his own image.”