God had long ago said that he would stand up for his people, claiming vengeance as his department (Deuteronomy 32:35, Deuteronomy 32:41, Deuteronomy 32:43). The conquerors characterize God as “just” in executing vengeance and “true” in doing so according to his promise.
3 And they sing the song of Moses, the servant of God, and the song of the Lamb, saying, “Great and amazing are your deeds, O Lord God the Almighty! Just and true are your ways, O King of the nations!