The covenant of grace partakes both of a testament and of a covenant. Hence it is not improperly called “a covenant by a testament,” “a testamentary covenant” and a “federal testament.” It is a covenant because after the manner of a covenant there was an agreement between parties and conditions were laid down on both sides, both on the part of God and on the part of man, and there was a mediator to reconcile the discordant parties. But it is also a “testament” (1) because it is a covenant in which an inheritance is promised (which necessarily demands the antecedent death of the testator, since he only then is reckoned an heir who obtains the goods by an intervention of the will of the disposer). Since therefore the covenant (diathēkē) is a promise (epangelia) of this kind (in virtue of which the inheritance is discerned), it must necessarily be testamentary. On this account, the apostle adds, “For where a diathēkē is [to wit, by which an inheritance is promised, i.e., a testament], there must also of necessity be the death of the testator.” (2) Because for our advantage only was this covenant made, as in a testament the advantage not of the testator but of the heirs is regarded; nor is God reconciled concerning mutual benefits, but concerning his own alone. (3) Because although conditions are set forth on both sides, they are entrusted for execution to the virtue and fidelity of only one party (namely, of God). Hence it is founded upon the mere grace of God and upon no disposition and merit of man (as will be fully proved in the proper place).
—Francis Turretin, Institutes of Elenctic Theology, ed. James T. Dennison Jr., trans. George Musgrave Giger (Phillipsburg, NJ: P&R Publishing, 1992–97), 12.1.3.