“O sing to the Lord a new song, for he has done marvelous things. His right hand and his holy arm have worked salvation for him.”
Clearly Psalm 98 is a psalm about salvation. The word “salvation” occurs three times in a consistent translation of the first three verses (KJV and others interpret the word salvation in verse 1 as “victory,” which blunts the force of the repetition). But it doesn’t give much detail about what you’re saved from, and it doesn’t go into detail about how you get saved. Instead it gives most of its attention to praising the savior, the God who accomplishes this salvation. God is named in this Psalm exactly seven times: 6 as Yahweh, and once as “our God.” And there are exactly seven mighty verbs of divine action, with exactly seven commands to praise God: Sing! Shout! Burst forth! Sing! Make music! Make music! Shout!
But we’ve been avoiding one obvious subject. When did this happen?
When did God do marvelous things? When did his right hand and holy arm work salvation for him? When did the Lord make known his salvation, and reveal his righteousness in the sight of the nations? When did God remember his grace and truth to the house of Israel? And when did all the ends of the earth see the salvation of our God? What specific historical action is this psalm calling on us to sing a new song about?
One possibility is that it’s referring to that paradigmatic event of salvation in the Old Testament, the Exodus. There is an event that God put himself into, that he used his right arm for, and that he is willing to be identified by: I am the Lord who brought you out of Egypt with a mighty hand and an outstretched arm. God certainly showed himself a victorious warrior there, remembered his grace and truth to Israel, and showed his righteousness to Pharoah and anybody who was watching. At the very least, this Psalm is using Exodus language to describe this salvation.
But the Psalm is not dated, and it might also be referring to the other end of Old Testament history, after Israel had been dispersed into exile. Maybe this Psalm was used by the generation that returned to the land and built the second temple. Again, it uses a lot of the language that you find in the last chapters of the book of Isaiah, who prophesies the return from exile and the restoration of Israel to a place of glory with God. Maybe the Psalm is prophetic like Isaiah, and is using the past tense to describe a future work of salvation.
So is it looking back to the Exodus or forward to the end of Exile? When do all the ends of the earth see the salvation of our God?
The medieval rabbis asked these questions, and in their commentaries on this Psalm they said that the new song will be sung “in the Messianic Age,” when “there will no longer be any troubles” and therefore this is a song “to be sung at the deliverance of Israel.” Rabbi Aha taught: “As long as the people of Israel are in exile, the right hand of the Holy One, blessed be He, is held in thrall, if one dare to speak thus. But when Israel is redeemed, mark that it is written His right hand and Holy arm, hath wrought deliverance for him.”
When did God reveal his righteousness? Another holy man of Israel thought he knew: in Luke 2:29, Simeon thinks he has seen the fulfillment of this Psalm, when he sees baby Jesus and says, “Lord, let your servant depart in peace, according to your word, for my eyes have seen your salvation, that you have prepared in the presence of all peoples, a light for revelation to the Gentiles, and for glory to your people Israel.”
So our two questions, “When did this happen?” and “why is this a Christmas psalm” answer each other. The Lord revealed his righteousness in the sight of the nations and remembered his lovingkindness to Israel in sending his Son, in the virginal conception, and in the birth in Bethlehem. Psalm 98 is a Christmas psalm because the salvation of our God was seen on Christmas day.