Psalm 133: Why are the mountains of Zion wet with Dew? And why is godly unity compared to that image?

Revelation 21:2 — Zion, the New Jerusalem, the holy city — she is the Church who was “prepared as a bride adorned for her husband.” Christ is the husband, and the Father has created the Church, the Bride. Therefore, the mountains of Zion are wet because she, the Church, is covered with the Dew-wetness of new birth. The Church is wet with Dew because she has been born by the regenerating work of the Spirit, she has left the womb, is wet with new birth and has been given to the Son.

Spirit and water are present and that is why godly unity exists between men who are wet with the waters of Baptism; men who are now united in Christ.