A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 48:1This is a spirited Psalm and song (compare Psa 30:1), having probably been suggested by the same occasion as the foregoing. It sets forth the privileges and blessings of God's spiritual dominion as the terror of the wicked and joy of the righteous. (Psa 48:1-14)
to be praised--always: it is an epithet, as in Psa 18:3.
mountain of his holiness--His Church (compare Isa 2:2-3; Isa 25:6-7, Isa 25:10); the sanctuary was erected first on Mount Zion, then (as the temple) on Moriah; hence the figure.
psa 48:2situation--literally, "elevation."
joy of, &c.--source of joy.
sides of the north--poetically for eminent, lofty, distinguished, as the ancients believed the north to be the highest part of the earth (compare Isa 14:13).
psa 48:3palaces--literally, "citadels."
refuge-- (Psa 9:10; Psa 18:3). He was so known in them because they enjoyed His presence.
psa 48:4For--The reason is given. Though the kings (perhaps of Moab and Ammon, compare Psa 83:3-5) combined, a conviction of God's presence with His people, evinced by the unusual courage with which the prophets (compare Ch2 20:12-20) had inspired them, seized on their minds, and smitten with sudden and intense alarm, they fled astonished.
psa 48:7ships of Tarshish--as engaged in a distant and lucrative trade, the most valuable. The phrase may illustrate God's control over all material agencies, whether their literal destruction be meant or not.
psa 48:8This present experience assures of that perpetual care which God extends to His Church.
psa 48:9thought of--literally, "compared," or considered, in respect of former dealings.
in the . . . temple--in acts of solemn worship (compare Ch2 20:28).
psa 48:10According . . . praise--that is, As Thy perfections manifested (compare Psa 8:1; Psa 20:1-7), demand praise, it shall be given, everywhere.
thy right hand, &c.--Thy righteous government is displayed by Thy power.
psa 48:11the daughters, &c.--the small towns, or the people, with the chief city, or rulers of the Church.
judgments--decisions and acts of right government.
psa 48:12The call to survey Zion, or the Church, as a fortified city, is designed to suggest "how well our God secures His fold." This security is perpetual, and its pledge is His guidance through this life.