Saying, This is the blood of the testament - Of the covenant; see notes on Hebrews 9:16-17. That is, this is the blood by which the covenant is ratified. It was the means used to confirm it; the sacred and solemn form by which it was made sure. When this was done, the covenant between God and the people was confirmed - as a covenant between man and man is when it is sealed.
Which God hath enjoined unto you - In Exodus 24:8, “which God hath made with you.” The language used by Paul, “which God hath enjoined” - ἐνετείλατο eneteilato - “commanded” - shows that he did not regard this as strictly of the nature of a “covenant,” or “compact.” When a compact is made between parties, one does not “enjoin” or “command” the other, but it is a mutual “agreement.” In the transactions between God and man, though called בּרית beriyt, or διαθήκη diathēkē, the idea of a “covenant” or “compact” is so far excluded that God never loses his right to “command” or “enjoin.” It is not a transaction between equals, or an “agreement;” it is a solemn “arrangement” on the part of God which he proposes to mankind, and which he enjoins them to embrace; which they are not indeed at liberty to disregard, but which when embraced is appropriately ratified by some solemn act on their part; compare notes on Hebrews 8:6.