The New extended the Old’s promises beyond the present life, and held out a sure hope of immortality

John Calvin writes,

“In the same way we infer that the Old Testament was both established by the free mercy of God and confirmed by the intercession of Christ. For the preaching of the Gospel declares nothing more than that sinners, without any merit of their own, are justified by the paternal indulgence of God. It is wholly summed up in Christ. Who, then, will presume to represent the Jews as destitute of Christ, when we know that they were parties to the Gospel covenant, which has its only foundation in Christ? Who will presume to make them aliens to the benefit of gratuitous salvation, when we know that they were instructed in the doctrine of justification by faith? And not to dwell on a point which is clear, we have the remarkable saying of our Lord, “Your father Abraham rejoiced to see my day, and he saw it and was glad,” (John 8:56). What Christ here declares of Abraham, an apostle shows to be applicable to all believers, when he says that Jesus Christ is the “same yesterday, to-day, and for ever,” (Heb. 13:8). For he is not there speaking merely of the eternal divinity of Christ, but of his power, of which believers had always full proof. Hence both the blessed Virgin²³¹ and Zachariah, in their hymns, say that the salvation revealed in Christ was a fulfilment of the mercy promised “to our fathers, to Abraham, and to his seed for ever,” (Luke 1:55, 72). If, by manifesting Christ, the Lord fulfilled his ancient oath, it cannot be denied that the subject of that oath²³² must ever have been Christ and eternal life.”