“It is as if the dew of Hermon were falling on Mount Zion.   For there the LORD bestows his blessing, even life forevermore.” (Psalms 133:3 NIV)
In the Bible we see dew bringing ‘life’ physically and metaphorically, for example,
“That evening quail came and covered the camp, and in the morning there was a layer of dew around the camp. When the dew was gone, thin flakes like frost on the ground appeared on the desert floor.” (Exodus 16:13–14 NIV)
“But your dead will live; their bodies will rise. You who dwell in the dust, wake up and shout for joy. Your dew is like the dew of the morning; the earth will give birth to her dead.” (Isaiah 26:19 NIV)
“I will be like the dew to Israel; he will blossom like a lily.” (Hosea 14:5 NIV)
The idea of this life-giving dew is played upon in Psalm 133. As the dew falls health flourishes – and the particular type of health in view here is unity.
The blessing is seen as falling specifically in Jerusalem (‘there’) in this Psalm. It is true that unity was found there, but, sadly, so was, later, the discord that would ultimately split the nation.
Perhaps the pilgrims of later days sang this Psalm more  in hope than celebration.  After Solomon’s death the northern tribes separated from Judah in the south, and no unity was possible for the next several hundred years. For most of this Psalm’s history it was sung by people who hoped for healing between the tribes. Little did they know that it was to come to mean something similar, but different to the followers of Messiah. Now we are one tribe, one nation, one people and unified by the king of kings (1 Peter 2:9Rev 19:16).
One sure way to heal disunified people is for each one to recognise that they have gifts available to one another.  More unity would be enjoyed if we looked for what we could contribute in serving others rather than seeking retribution and redress. Hermon, the chief mountain of (northern) Israel had a resource that Zion, the mountain of (southern) Judah needed.
“Dew” can also mean light rain or drizzle. Hermon’s summit is well watered. It is 2,814 m high and you will find  snow up there all year.  There is such a heavy dew at high altitudes that a night in the open air will see you thoroughly drenched in the morning. Steams flow down the mountain, unlike Zion which is dry as a bone. If the one with the resource shares it with the one in need, then both will be refreshed.
This is a good reminder to us that unity is never a passive entity, but a dynamic one – tending towards greater harmony or chaos depending on the conduct of the people of God.
“Make every effort to keep the unity of the Spirit through the bond of peace.” (Ephesians 4:3 NIV)
What gift can you offer another that will heal & unify?