This is my blood of the new testament, which is poured out for many for the forgiveness of sins. (Matthew 26:28, EHV)
As Luther reflects on God’s promise that aging Abraham would have a son by his aging wife, Sarah, his throughts turn to the testament we have received in Lord’s Supper.
[Holy Communion] is a promise of the forgiveness of sins made to us by God. Such a promise as has been confirmed by the death of the Son of God.
The only difference between a promise and a testament is that the testament involves the death of the one who makes it. A testator is a promiser who is about to die, while a promiser (if I may put it thus) is a testator who is not about to die.
This testament of Christ is foreshadowed in all the promises of God from the beginning of the world. Indeed, whatever value those ancient promises possessed was altogether derived from this new promise that was to come in Christ.
Hence the words “compact,” “covenant,” and “testament of the Lord” occur so frequently in the Scriptures.
These words signified that God would one day die. “For where there is a testament, the death of the testator must of necessity occur” (Hebrews 9[: 16]).
Now God made a testament; therefore, it was necessary that he should die. But God could not die unless he became man. Thus the incarnation and the death of Christ are both comprehended most concisely in this one word, “testament.” …
[Access to God’s promise is] gained, not with any works, or powers, or merits of one’s own, but by faith alone. For where there is the Word of the promising God, there must necessarily be the faith of the accepting man. It is plain, therefore, that the beginning of our salvation is a faith which clings to the Word of the promising God, who, without any effort on our part, in free and unmerited mercy, takes the initiative and offers us the word of his promise.
Source: Luther’s Works, vol. 4: Lectures on Genesis: Chapters 21-25.