And it shall come to pass in that day, that the mountains shall drop down sweetness, and the hills shall flow with milk: and waters shall flow through all the rivers of Juda: and a fountain shall come forth of the house of the Lord, and shall water the torrent of thorns (Joel 3:18).

In those days, Scripture says, the mountains will give forth fragrance and the hills flow with milk, and water ­shall run through all the rivers of Judah.

The mountains of that country are the Prophets and the Apostles; the hills are the other Saints, whose teaching ordinary people have humbly taken in and for that reason received a share of their glory…, and on which indeed they draw by their daily contact.

For they will behold God’s glory more fully in those people from whom they have come to know God’s teach­ing.

[…] The mountains shall exude fragrance and the hills flow with milk; and through all the rivers of Judah – that is to say, through the hearts of the faithful confessing Christ – shall waters gush to life eternal.

Yet of the same fragrance, of the same milk, of the same waters the one spring shall lead forth through the mountains and the hills, and through all the rivers from the Lord’s house….

The house is rightly understood to be Christ’s body: for that in itself is the house which wisdom has built for itself, or for herself.

And so we read that: the spring shall lead forth from the Lord’s house, and shall water a bed thick with thorns:

the source of all life and the torrent of joy welling up and leading forth from the Lord’s house shall indeed swell a river, a torrent running over thorns: that really means, the realm of God’s chosen ones.

There shall be what before there was not, from East to West amongst the thorns of tribulation and sin; what is now a torrent of delights, abounding with the plenty of eternal good cheer.

Of this, we read in the Apocalypse: And he showed me a river of running water, clear as crystal, flowing from the seat of God and the Lamb, amidst a city plain.

And from both sides of the river the tree of life, bearing twelve fruits, each month yielding its own.

We should note that this is the spring, the river, of the Holy Spirit, who says, speaking through the Prophet:

Behold, I flow down and run through them like a river of peace and tranquillity, like a gushing torrent, for the glory of the people.

This river of peace, I say, this torrent of glory, this river of rejoicing, this torrent of pleasure, this abundance of God’s house – this is the Holy Spirit.

For he is the love of bride and groom, whereby what was a mass of thorns is irrigated, enlivened, healed, and refreshed, to become a torrent of delights.

That is our human condition: mortal and wretched as it was, now become immortal and blessed.

Rupert of Deutz (c.1075–1129): Commentary on Joel, from the Monastic Office of Vigils for Thursday of the Eighteenth Week in Ordinary Time, Year 2.