In his Reflections on the Psalms, C.S. Lewis implies that modern Christians often miss a crucial aspect of the nativity. In celebrating the peace and joy that the infant Jesus embodies for Israel and for the world it is easy to lose sight of his combined priest-kingly activity of “binding the strong man” and destroying the powers of evil that have kept God’s people in darkness. Lewis writes:
We find in our Prayer Book that Psalm 110 is one of those appointed for Christmas Day. We may at first be surprised by this. There is nothing in it about peace and goodwill, nothing remotely suggestive of the stable at Bethlehem. It seems to have been originally either a coronation ode for a new king, promising conquest and empire, or a poem addressed to some king on the eve of a war, promising victory. It is full of threats. The ‘rod’ of the king’s power is to go forth from Jerusalem, foreign kings are to be wounded, battle fields to be covered with carnage, skulls cracked. The note is not ‘Peace and goodwill’ but ‘Beware. He’s coming.’1
Lewis explains that there are two things that attach Psalm 110 to Christ “with an authority far beyond that of the Prayer Book”:
The first of course … is that He Himself did so; He is the ‘lord’ whom ‘David’ calls ‘my Lord.’ The second is the reference to Melchizedek (v. 4). The identification of this very mysterious person as a symbol or prophecy of Christ is made in Hebrews 7 […] He comes from nowhere, blesses in the name of the ‘most high God, possessor of heaven and earth,’ and utterly disappears. This gives him the effect of belonging, if not to the Other World, at any rate to another world; other than the story of Abraham in general. He assumes without question, as the writer of Hebrews saw, a superiority over Abraham which Abraham accepts. He is an august, a ‘numinous’ figure. […] The episode of Melchizedek … puts in, with unforgettable impressiveness, the idea of a priesthood, not Pagan but a priesthood to the one God, far earlier than the Jewish priesthood which descends from Aaron, independent of the call to Abraham, somehow superior to Abraham’s vocation. And this older pre-Judaic, priesthood is united with royalty; Melchizedek is a priest-king. In some communities priest-kings were normal, but not in Israel. It is thus simply a fact that Melchizedek resembles (in his peculiar way he is the only Old Testament character who resembles) Christ Himself. For He, like Melchizedek, claims to be Priest, though not of the priestly tribe, and also King. Melchizedek really does point to Him; and so of course does the hero of Psalm 110 who is a king but also has the same sort of priesthood … For a Jewish convert to Christianity this was extremely important and removed a difficulty. He might be brought to see how Christ was the successor of David; it would be impossible to say that He was, in a similar sense, the successor of Aaron. The idea of His priesthood therefore involved the recognition of a priesthood independent of and superior to Aaron’s. Melchizedek was there to give this conception the sanction of the Scriptures.
Lastly, Lewis explains how certain Christmas Psalms combine the concepts of priest and king and what this means for modern Christians:
For us Gentile Christians it is rather the other way around. We are more likely to start from the priestly, sacrificial, intercessory character of Christ and under-stress that of king and conqueror. Psalm 110, with three other Christmas Psalms, corrects this. In 45 we have again the almost threatening tone: ‘Gird thee with thy sword upon thy thigh, O thou most mighty … they right hand shall teach thee terrible things … they arrows are very sharp’ (vv. 4-6). In 89 we have the promises to David (who would certainly mean all, or any, of David’s successors, just as ‘Jacob’ can mean all his descendants). Foes are to fall before him (v. 24). ‘David’ will call God ‘Father,’ and God says ‘I will make him my first-born’ (vv. 27-28), that is ‘I will make him an eldest son,’ make him my heir, give him the whole world. In 132 we have ‘David’ again; ‘As for his enemies, I shall clothe them with shame, but upon himself shall his crown flourish’ (v. 19). All this emphasizes an aspect of the Nativity to which our later sentiment about Christmas (excellent in itself) does less than justice. For those who first read these Psalms as poems about the birth of Christ, that birth primarily meant something very militant; the hero, the ‘judge’ or champion or giant-killer, who was to fight and beat death, hell and the devils, had at last arrived, and the evidence suggests that Our Lord also thought of Himself in those terms.
According to Lewis, Milton’s poem on the nativity encapsulates the idea of the baby Jesus as a conquering priest-king. Among other images, Milton recounts:
He [Osiris] feels from Juda’s land
The dredded Infants hand,
The rayes of Bethlehem blind his dusky eyn;
Nor all the gods beside,
Longer dare abide,
Nor Typhon huge ending in snaky twine:
Our Babe, to shew his Godhead true,
Can in his swadling bands controul the damned crew.