Albert Barnes Commentary Psalms 102:22

"When the peoples are gathered together, And the kingdoms, to serve Jehovah." — Psalms 102:22 (ASV)

When the people are gathered together—When they will be brought from their dispersion in distant lands; when they will assemble again in the city of their fathers, and when public worship will be celebrated there as in former ages.

And the kingdoms, to serve the Lord—The Septuagint and the Latin Vulgate render this, “kings.” The reference must be to the time when those of other lands—kings and their people—would be converted to the true religion; when the Gentiles as well as the Jews, then one undistinguished people, would be brought to the knowledge of the true God, and would unite in His worship. See the notes at (Isaiah 60:0). All of all lands, will yet praise the Lord as if they were one great congregation, assembled in one place. Thus, though separate, they will with united feeling recount the mercy and goodness of God to His people in past times.