God will hold the people to whom Jesus is speaking responsible for the murder of the prophets by their ancestors. Alternate translation: "God will hold this generation responsible for the deaths of all the prophets whom people have killed since the foundation of the world" (See: [[rc://en/ta/man/jit/figs-activepassive]])
The "blood ... shed" refers to the blood that was spilled when the prophets were killed. Alternate translation: "for all the murders of the prophets" (See: [[rc://en/ta/man/jit/figs-metonymy]])
The author speaks of the world as if it were a building set on a foundation. Alternate translation: "since the creation of the world" or "since God created the world" (See: [[rc://en/ta/man/jit/figs-metaphor]])