Joel 3:18 - Matthew Poole's English Annotations on the Holy Bible

In that day; when afflictions, amidst which they were preserved, from which delivered, and by which they were purified. The mountains; the vines planted upon the mountains, which were dried up, Joel 1:12, shall now be full of juice and fruit. Shall drop down, shall come down as the showers or dew, sweetly and plentifully, new wine; sweet and delicious. The hills shall flow with milk; so fruitful shall the hills be, and keep so many cows, sheep, and goats, that milk shall abound every where, as it were a current that ever runs down. All the rivers of Judah shall flow with waters: in the great drought rivers dried up, now the rivers shall be full of water and ever flow. A fountain: the prophet alludes to those waters which were conveyed from some spring through conduit pipes towards the altar, of which Ezekiel 47:1-5, for the use of the temple, in which water the priests washed what was to be washed. This no doubt is a shadow of the purifying blood of Christ, and his sanctifying Spirit and word. And in that it is said to come from the house of the Lord, it intimateth that these glad tidings, this saving grace, shall be first preached from Jerusalem, and by the church, which is the house of God, shall be published to others. Shall water, refresh, purge, and make fruitful in all holy works, the valley of Shittim; it was a place in the plains of Moab, on the borders of Israel towards the south-east, Numbers 33:49 Joshua 3:1, not far from the Dead Sea. These spiritual waters shall flow down to the dry and thirsty, the barren and fruitless Gentiles, and make them fruitful.