Taken from this paper on Luther's exegesis of Genesis 3...
The meaning is Christ
Rescuing the Scriptures from the Judaizers
‘Christ is the Lord, not the servant, the Lord of the Sabbath, of law, of all things. The Scriptures must be understood in favour of Christ, not against Him. For that reason they must either refer to Him or must not be held to be true Scripture.’ (LW34.112)
When Luther says ‘must’ in this quotation he is deadly serious. The written Word is a servant of the Eternal Word. We cannot know God except "clothed in His Word and promises , so that from the name ‘God’ we cannot exclude Christ, whom God promised to Adam and the other patriarchs." (Commentary on Psalm 51, 1532).
Luther constantly returns to Genesis 3:15 as the promise by which Adam and Eve laid hold of life, and the fountainhead of all gospel promise:
"This, therefore is the text that made Adam and Eve alive and brought them back from death into the life which they had lost through sin." (LW1.196-7)
"Never will the conscience trust in God unless it can be sure of God’s mercy and promises in Christ. Now all the promises of God lead back to the first promise concerning Christ: “And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.” The faith of the fathers in the Old Testament era, and our faith in the New Testament are one and the same faith in Christ Jesus, although times and conditions may differ... The faith of the fathers was directed at the Christ who was to come, while ours rests in the Christ who has come. Time does not change the object of true faith, or the Holy Spirit. There has always been and always will be one mind, one impression, one faith concerning Christ among true believers whether they live in times past, now, or in times to come. We too believe in the Christ to come as the fathers did in the Old Testament, for we look for Christ to come again on the last day to judge the quick and the dead. (Galatians commentary, 3:6)
Luther came to Genesis not primarily seeking for grammatical and historical understanding, but seeking for Christ. As he claimed above, ‘the Scriptures must be understood in favour of Christ.' For Luther, distinguishing the Church from Old Testament Israel has never been a question of adding a new, retrospectively awarded meaning to Moses. The method modelled by Jesus and His Apostles has been to declare the inherent Messianic proclamation of all Biblical revelation. Luther is completely in line with this as he repeatedly champions Genesis 3:15, not simply here, but throughout his work. Yet this confidence in the protevangelium has sounded ‘incautious’ and ‘unreal’ to more modern ears.
F. Farrar in his History of Interpretation says this:
“When Luther reads the doctrines of the Trinity, and the Incarnation, and Justification by Faith, and Reformation dogmatics and polemics, into passages written more than a thousand years before the Christian era… he is adopting an unreal method which had been rejected a millennium earlier by the clearer insight and more unbiased wisdom of the School of Antioch. As a consequence of this method, in his commentary on Genesis he adds nothing to Lyra except a misplaced dogmatic treatment of patriarchal history.” (p334)
Farrar misunderstands both Luther’s exegesis and his exegetical convictions. Luther is not claiming to read back into the text a Christological reinterpretation. His claim is that the gospel of Christ was preached, understood, trusted and passed on by the faithful throughout the Old Testament era. His convictions in making such a claim are that non-Christological interpretations are really non-interpretations. The written Word must preach the Eternal Word or it is no word worth hearing. It is worth noting though that this prior commitment also allows Luther to make the greatest sense of the literal, historical and grammatical content of the passage.
In this respect Calvin is often seen as a more 'cautious' foil to Luther's christocentric bias.
So R. Grant in A Short History of the Interpretation of the Bible writes:
‘Not all the reformers carried the principles of Reformation exegesis to the conclusion which Luther reached. John Calvin, for example, vigorously maintains an ‘objective’ type of interpretation. For him, scripture itself is the authority for Christian belief, rather than any Christocentric interpretation of scripture.’ (p106, emphasis mine)
That seems a very fair assessment. And one worth ruminating upon.
Gerald Bray in Biblical Interpretation: past and present has written similarly:
“As an exegete Calvin is noted for his scrupulous honesty; he resisted the temptation to read Christological meanings into even such ‘obvious’ passages as Genesis 3:15.” (p203, emphasis mine)
Calvin’s principles of Old Testament interpretation as laid out in the Institutes (e.g. I.13; II.9-11) are admirable. Yet they are not followed through with consistency in his expositions. For instance, neither the Trinitarian (1:1,26; 3:22) nor Christological points (3:15) are picked up in Calvin’s Genesis commentary.
Lutherans in the 17th century felt so strongly about Calvin’s Old Testament exegesis that anathemas were pronounced, most notably by Aegidius Hunnius, in his Calvinus Judaizans (Wittenberg, 1693). While this was a definite over-reaction it certainly points to differing trajectories and a tendency in Calvin to underplay that on which Luther had so passionately insisted.
In our own age, evangelical scholarship is crying out for defenders of a Christian Old Testament. In John Sailhamer's excellent article The Messiah and the Hebrew Bible, he quotes Walter Kaiser as saying:
“if [the Gospel] is not in the Old Testament text, who cares how ingenious later writers are in their ability to reload the OT text with truths that it never claimed or revealed in the first place? The issue is more than hermeneutics… [the issue is that of] the authority and content of revelation itself!”
Gordon McConville comments in the same article
“the validity of a Christian understanding of the Old Testament must depend in the last analysis on [the] cogency of the argument that the Old Testament is messianic.”
We ought to re-learn from Luther the Christian meaning of Moses and the Prophets. Not that, now Moses can be read through Christian spectacles. Rather, that the only spectacles through which Scripture can be read are Christian. The issue with our modern Jewish friends is not about whether the New Testament is a valid addition and re-interpretation of the Old. The issue is the Old Testament itself. We must maintain that the Hebrew Scriptures in and of themselves are Christian Scripture written from faith in Christ and directed to evoke faith in Christ (cf. 2 Tim 3:15-17; Acts 10:36,43). Luther would be an excellent tutor for our modern age in reclaiming the Hebrew Scriptures for Jesus.