John Gill Commentary Psalms 99:9

"Exalt ye Jehovah our God, And worship at his holy hill; For Jehovah our God is holy." — Psalms 99:9 (ASV)

Exalt the Lord our God
Having given the above instances of Moses, Aaron, and Samuel, serving and worshipping the Lord, the psalmist repeats the exhortation in (Psalms 99:5), which he enforces by their example; (See Gill on Psalms 99:5):

and worship at his holy hill ;
the holy hill of Zion, the church; attend the public worship and service of it: the Targum is,

``worship at the mountain of the house of his sanctuary; the temple, a type of the church of Christ:''

for the Lord our God is holy ;
his nature is holy, and he is glorious in the perfection of his holiness, and therefore to be praised and exalted; and his name is holy, and so reverend, and therefore to be worshipped; see in (Psalms 99:3Psalms 99:5) .