Albert Barnes Commentary Psalms 68:26

"Bless ye God in the congregations, Even the Lord, [ye that are] of the fountain of Israel." — Psalms 68:26 (ASV)

Bless ye God in the congregations - In the assemblages of the people; not only as individuals, but in solemn processions; in triumphal marches; when the people are assembled together. In this public manner acknowledge God as the true God, and render him praise.

Even the Lord, from the fountain of Israel - Margin, “Ye that are of;” that is, “of the fountain of Israel.” The margin has undoubtedly expressed the correct idea. The appeal is to the Hebrew people represented as descending from a common stock or ancestor—Jacob or Israel—as a stream or river flows from a fountain. Compare the notes on Isaiah 48:1; see also Isaiah 51:1; Deuteronomy 33:28. All the descendants of Jacob or Israel are thus called on to unite in solemnly praising the Lord their God.