John Calvin Commentary Psalms 87:1

"His foundation is in the holy mountains." — Psalms 87:1 (ASV)

His foundations are in the holy mountains. Those who understand that Jerusalem is meant here, as if it were said to be founded upon the holy mountains, are, in my judgment, mistaken, for the relative is in the masculine gender. I am aware that some learned men defend this opinion by supposing that the words the people are to be supplied, even though the capital of Judea is specified.

But I do not need to say anything to prove what is apparent to everyone: that this interpretation is forced. Some Jewish interpreters have considered it most probable that this opening sentence refers to the psalm itself. Accordingly, they explain foundations as metaphorically denoting the theme, or subject of the poem, because it concerns the holy city Jerusalem, which was situated on mountains.

But I am surprised that they could have been mistaken in such an obvious matter. Since it is quite common among the Hebrews to use a relative pronoun without its antecedent, this way of speaking should not seem harsh or strange. The name of God is mentioned a little later, and we know that He is everywhere represented as having founded Jerusalem.

Some understand the mountains to mean Moriah and Zion, which were the two peaks of a mountain split in two, but this interpretation is too forced. Since the country was mountainous, we should rather understand that the prophet had in mind the various neighboring and contiguous mountains that formed a chain around Jerusalem; for we will see in another place that Jerusalem was surrounded by mountains (Psalms 125:2).

The true and natural meaning, then, is that God chose the holy mountains to found and establish His city in their midst. For a little later, in the continuation of the subject, these words occur: The Highest himself shall establish her. He is indeed the founder of other cities as well, yet we do not read of Him saying this concerning any other city:

This is my rest for ever; here will I dwell; for I have desired it,
(Psalms 132:14).

There is this difference, which must always be remembered: while other cities were founded and built by the guidance and power of God merely for the sake of civil government, Jerusalem was His unique sanctuary and His royal seat. Isaiah also uses a similar expression (Isaiah 14:32): The Lord hath founded Zion, and the poor of his people shall trust in it.

Besides, although the whole country of Judea was consecrated to God, yet He is said to have rejected all the other cities and to have chosen this one for Himself in which to reign. Here the question is not about earthly polity but spiritual government, for the pure religion, the true worship of God, and the doctrine of godliness could at that time be found only in Jerusalem.