Psalms 135:21

Blessed be the LORD out of Zion, which dwelleth at Jerusalem. Praise ye the LORD.

Blessed be the Lord from Zion who dwells at Jerusalem belongs to a group of devotional psalms. Those psalms are largely occupied with praising Jehovah for His loving-kindness and tender mercy. That loving-kindness and tender mercy endure forever, and the verse gives voice to the response they call forth by summoning all to praise the Lord.