Psalm 99 has no title and is often seen as the last of the psalms that open, Yahweh reigns! It is built around a refrain that grows: He is Holy! in verses 3 and 5, and then, for Yahweh, our God, is holy! in verse 9. The picture of God enthroned among the cherubim recalls the ark of the covenant, where golden cherubim spread their wings over the place God met his people.
God's holiness is not distant. It shows in justice: The King's strength also loves justice. You establish equity. You execute justice and righteousness in Jacob. His power is used for what is right. The call is to exalt Yahweh our God and worship at his footstool, the ark or the temple on earth where the King of heaven chose to meet with his people.
The last section remembers Moses and Aaron, who were among his priests, and Samuel, who called on his name. They called on Yahweh, and he answered them. He spoke to them in the pillar of cloud. Verse 8 holds two truths together: You are a God who forgave them, although you took vengeance for their doings. God's forgiveness does not erase his discipline. The psalm ends, Exalt Yahweh, our God. Worship at his holy hill, for Yahweh, our God, is holy!