like the dew of Hermon, that comes down on the hills of Zion: for there Yahweh gives the blessing, even life forever more.
As the dew of Hermon, and as the dew that descended upon the mountains of Zion. From the loftier mountains the moisture appears to be wafted to the lesser hills: the dews of Hermon fall on Zion. The Alpine Lebanon ministers to the minor elevation of the city of David; and so does brotherly love descend from the higher to the lower, refreshing and enlivening in its course.
The Psalm celebrates the gathered fellowship of God's people united for worship at one sanctuary, the joy that Israel experienced during the great Feasts. When brethren united by blood and heart come together in this way, it is a blessed communion that expresses their true nature in outward reality.
AI summary
Commenting on Psalm 133:1-3
As the dew of Hermon, [and as the dew] that descended upon the mountains of Zion: for there the LORD commanded the blessing, [even] life for evermore. (c) By Hermon and Zion he means the plentiful country about Jerusalem. (d) Where there is such concord.