Let us sing to the Lord, great is his renown! Horse and rider he has thrown into the sea.
It is common knowledge that the song of Moses recorded in the Book of Exodus can be understood in a spiritual sense as pointing forward to the Gospel teaching on regeneration.
[...] The author of the Apocalypse is therefore correct in describing the hymn sung by the saints in heaven as the song of Moses, the servant of God, and the song of the Lamb.
By giving it this title, he is linking together a historical event and a spiritual reality.
The crossing of the sea under the leadership of Moses is seen as a foreshadowing of what Christ, the Lamb of God, does for us in the regenerating waters of Baptism.
‘Lamb of God’ is used here as a richly evocative designation for the son of God, into whose death we have been baptized.
When Moses first intoned his song, he did so in honour of an event that had begun with the slaying of a lamb.
God himself had ordained that on the evening of the fourteenth day of the first month a lamb should be sacrificed.
The slaughter of that lamb prefigured the death of Christ, the Son of God, who was destined to be slain in expiation of our sins.
[...] The saints, therefore, are described as singing the song of Moses because they resemble Moses both in their singing and in the subject matter of their song.
But while they too praise the Lord with joy and thanksgiving to the accompaniment of harps, their song consists of one short verse only.
This single verse contains none the less two all-important themes: the power of God and the justice of the Eternal King.
Great and wonderful are your deeds is a proclamation of God’s power. Just and true are your ways is an acknowledgement of his justice.
Of the two it is surely more meritorious to confess the second than the first. If we fear and praise God as the most powerful of spirits because we witness his marvellous deeds, our confession is certainly not lacking in merit.
But if we can discern the divine justice underlying these same deeds and strenuously uphold it in the face of every denial, we shall gain a far greater blessing.
And the same is true even when discernment fails us: we are blessed indeed if we still bow down in loving adoration of God’s justice, worshiping him in the words the Apostle Paul teaches each one of us to say:
O the depths of the riches and wisdom and knowledge of God! How incomprehensible are his judgments, how unfathomable his designs!
Rupert of Deutz (c.1075–1129): In Apoc. 9.15 (PL 169:1109-1110); from the Monastic Office of Vigils for Wednesday of the 4th Week in Eastertide, Year 1.