20. Ex 24:8, "Behold the blood of the covenant, which the Lord has made with you concerning all these words." The change is here made to accord with Christ's inauguration of the new testament, or covenant, as recorded in Lu 22:20, "This cup (is) the new Testament in My blood, which is shed for you": the only Gospel in which the "is" has to be supplied. Luke was Paul's companion, which accounts for the correspondence, as here too "is" has to be supplied.
      testament--(See on Heb 9:16, 17). The Greek "diathece" means both "testament" and "covenant": the term "covenant" better suits the old dispensation, though the idea testament is included, for the old was one in its typical relation to the new dispensation, to which the term "testament" is better suited. Christ has sealed the testament with His blood, of which the Lord's Supper is the sacramental sign. The testator was represented by the animals slain in the old dispensation. In both dispensations the inheritance was bequeathed: in the new by One who has come in person and died; in the old by the same one, only typically and ceremonially present. See ALFORD'S excellent Note.
      enjoined unto you--commissioned me to ratify in relation to you. In the old dispensation the condition to be fulfilled on the people's part is implied in the words, Ex 24:8, "(Lord made with you) concerning all these words." But here Paul omits this clause, as he includes the fulfilment of this condition of obedience to "all these words" in the new covenant, as part of God's promise, in Heb 8:8, 10, 12, whereby Christ fulfils all for our justification, and will enable us by putting His Spirit in us to fulfil all in our now progressive, and finally complete, sanctification.

JFB.