John Gills Exposition of the Bible Commentary - Psalms 87:1
His foundation is in the holy mountains. The Jewish writers connect these words with the title of the psalm, and make the sense to be this; "the foundation" or argument "of it", the psalm, "is concerning the holy mountains" of Zion and Jerusalem; so Aben Ezra, Jarchi, and Kimchi; and the Targum joins them together thus, "by the hands of the sons of Korah is said a song, which is founded by the mouth of the fathers that were of old:' but the words are a part of the song or psalm, which... read more
Matthew Henry's Complete Commentary - Psalms 87:1-3
Some make the first words of the psalm to be part of the title; it is a psalm or song whose subject is the holy mountains?the temple built in Zion upon Mount Moriah. This is the foundation of the argument, or beginning of the psalm. Or we may suppose the psalmist had now the tabernacle or temple in view and was contemplating the glories of it, and at length he breaks out into this expression, which has reference, though not to what he had written before, yet to what he had thought of; every... read more