Matthew Poole and continuators on Hebrews 9:17

17 For a Testament is of force after men are dead: otherwise it is of no strength at all whilst the Testator liveth.

The Testator being by Death disseised of his Goods and Lands, the right takes place of the Legatees, and the time of their challenging it; such a sacred Tie there is upon the surviving, that none can of right add to it, alter, or disannul it.

It is of no force while the maker of it liveth, because they have need of the things bequeathed; they can alter and change it, and by the Will it self it is declared none shall have any right to the things bequeathed in it till the Testator be dead. The consequent of all this is, That the Testator of the New Testament must put it in force by Death; and his Death is of greater force to confirm his Testament than that of Men, because his Will can never be violated, it being a Divine Constitution, but the human Testament may. Christ God-Man after dieth, as Testator, and puts the Testament in force; and by breaking the bonds of Death, doth gloriously effect that the Legatees perform the Conditions required in the Will, to fit them for receiving their Legacies; and then faithfully distributeth them to them by his grand Executor the Holy Spirit, who applieth the virtue of it to the Legatees under the Old Testament, as well as these under the New; He being the Testator, as well as the Lamb slain from the beginning of the World.

Marginal references: Gal. 3.15.