His foundation - This is an abrupt commencement of the psalm. The adjective “his” has been supposed by some to refer to the psalm itself, and this expression has been considered to be a part of the title to the psalm, meaning that the foundation of the psalm is the holy mountain where the praises of God were celebrated; that is Zion. This, however, is a forced and unnatural interpretation. The most obvious explanation is to refer it to God, and the meaning is, that his “foundation,” or that which he had founded and established, to wit, the place for his worship, or for the institutions of religion, was in the holy mountains of Jerusalem. It would seem that the psalmist was contemplating the city - looking on its walls, and its palaces, and especially on the place which had been reared for the worship of God, and that he breaks out in this abrupt manner, by saying that this was what God had founded; that here he had established his home; that here was the place where he was worshipped, and where he dwelt; that this was the place which he loved more than all the other places where the descendants of Jacob dwelt.
Is in the holy mountains - The mountains of Jerusalem. Jerusalem is surrounded by hills, and within the city itself there were the hills of Zion, Moriah, Acra, and Bezethah; See the notes at Matthew 2:1. These sacred hills God had selected as the place of his solemn worship - of his own abode. Compare the notes at Psalms 48:1-2.