Isaiah 9:2–7 is among the most familiar of the Advent prophecies, but its content is a claim about headship and government, not merely comfort: the government shall be upon his shoulder, and his name shall be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace. Of the increase of his government and of peace there will be no end. Formula of Concord, Solid Declaration, Article VIII, reads this text as a direct statement about the person of Christ: a government carried on the shoulder of a child born, a son given, is a government exercised by One who is simultaneously Mighty God, meaning the peace this king establishes is not the peace of a merely human administration.
Psalm 45 is a royal wedding psalm addressed to a king whose throne, the psalm says explicitly, is forever and ever, and who is addressed directly as God: your throne, O God, is forever and ever. FC VIII treats this identification as scriptural warrant for the same claim Isaiah 9 makes: a human king who is also addressed as God. The Formula's Christological argument in Article VIII depends on holding these two psalms and prophecies together without diluting either the humanity or the deity, because the peace Isaiah 9 promises can only be as everlasting as the government is divine, and the government can only be divine if the person exercising it is genuinely, fully God even while genuinely, fully the child born, the son given.
| Term | What It Means |
|---|---|
| Personal union | FC VIII's term for the union of the divine and human natures in the one person of Christ, joined without confusion, change, division, or separation, from the moment of conception. Not two persons cooperating, but one person possessing two distinct natures. |
| Communicatio idiomatum | The communication of attributes: because the two natures are united in one person, the properties of each nature are truly attributed to the one person of Christ. The Son of Man can therefore be said to have all power in heaven and on earth, not because the human nature independently possesses it, but because the person who possesses it is also true God. |
| Genus majestaticum | The specific mode of the communication of attributes by which the divine majesty, power, and glory are communicated to the human nature of Christ, so that the man Jesus, in and according to his humanity, has been placed at the right hand of God's majesty and power. |
| The government upon his shoulder | Isaiah 9:6's image, read by FC VIII as the human nature of Christ, the child born, exercising a divine, everlasting government because of its personal union with the Mighty God. The shoulder that bears the government is the same shoulder that would later bear the cross. |
Isaiah 9:6's structure is deliberately jarring: for to us a child is born, to us a son is given, and the government shall be upon his shoulder. The verbs are the plainest possible language of human birth, a child born, a son given, and yet the noun immediately following is government, and the names that follow the noun are not human titles: Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace. FC VIII reads this juxtaposition as exactly the claim Christian confession must make and refuse to soften in either direction: this is a genuine human birth, and the one born is genuinely called Mighty God in the same breath.
The Formula's broader argument in Article VIII is aimed at two errors that each resolve the tension by eliminating one side of it. One error effectively separates the natures so completely that the human nature of Christ becomes, in practice, a mere instrument or garment worn by the divine nature, with no real exchange of properties between them. The opposite error blends the natures into a third thing, neither fully God nor fully man. Isaiah 9:6 resists both errors simply by refusing to choose: the child born bears the government, and the government belongs to Mighty God, and these are not two separate claims about two separate subjects but one claim about one person.
Psalm 45 was composed as a royal wedding song, and its address to the king in verse 6 has occupied commentators for as long as the psalm has been read: your throne, O God, is forever and ever; the scepter of your kingdom is a scepter of uprightness. The plain sense of the Hebrew text addresses a human king, anointed, seated on an earthly throne, in the second person as God. FC VIII draws on this text as further scriptural confirmation that Scripture itself does not treat the ascription of divine identity to an enthroned human king as a category error, but as the appropriate address to a king whose throne, unlike every other throne in Israel's history, is genuinely forever and ever.
The Formula's use of Psalm 45 alongside Isaiah 9 is not incidental. Both texts insist on holding together a human office, a birth, a wedding, a throne, an anointing, with a divine identification that makes the promised permanence of that office credible. Every merely human throne in Israel's history eventually fell, including David's own. Psalm 45's claim that this throne is forever and ever only makes sense if the king seated on it possesses, by personal union, the eternity that belongs to God alone. The peace Isaiah 9 promises without end depends on exactly this: a throne occupied by someone who cannot be deposed by death, time, or a rival dynasty, because the person on it is Mighty God as well as son of David.
FC VIII's technical vocabulary, the personal union, the communicatio idiomatum, the genus majestaticum, exists to protect a specific pastoral good: that the human nature of Christ genuinely, not merely nominally, shares in the government, majesty, and power that Isaiah 9 and Psalm 45 describe. The government upon his shoulder in Isaiah 9:6 and the shoulder that would later carry the cross to Golgotha are not two different shoulders belonging to two different aspects of Christ that happen to share a body. They are the same shoulder, belonging to the same person, exercising real dominion even at the moment that same shoulder is bent under the weight of an instrument of Roman execution.
This is why FC VIII insists that the attributes are genuinely communicated to the one person and not merely predicated of two natures side by side. If the human nature of Christ merely stood next to an unaffected divine nature, then the government upon his shoulder would be a metaphor, and the peace it establishes would be an abstraction imposed from outside human experience rather than a peace won from within it, by a man who bled, by God who cannot bleed, united in one person who did both at once. The increase of his government and of peace shall have no end because the person exercising that government is the same person who conquered the one thing that ends every other government: death itself.
The government upon his shoulder in Isaiah 9:6 became, within the same lifetime the prophecy anticipated, the wood of a cross laid upon that same shoulder on the road to Golgotha, borne by the very person Psalm 45 addresses as God whose throne is forever and ever. The increase of his government and of peace has no end precisely because the child born and the Mighty God are the same undivided person, and the peace he purchased on that shoulder was not a peace negotiated between two parties but a peace won from within human suffering by the only king whose throne death itself could not end.