Jeremiah 13:2

The blessed John disdained sheep's wool because it savored of luxury; he preferred camel's hair and clothed himself in it, giving us an example of simple, frugal living. Incidentally, he also ate only honey and locusts, food that is sweet and with a spiritual significance. So it was that he prepared the way of the Lord and kept it humble and chaste. He fled from the false pretenses of the city and led a peaceful life in the desert with God, away from all vanity, boasting and servitude. How could he possibly have worn a purple mantle? Elijah used a sheepskin for his garment and girded it tight with a belt made of leather. Isaiah, another historic prophet, went "naked and without sandals" and often put on sackcloth as a garment of humility. If you protest and make mention of Jeremiah, he wore only a loincloth made of linen.

After these things let us look at what concerns the loincloth. For "Thus," it says, "says the Lord: Go and acquire for yourself a linen loincloth, and put it around your loins, and do not pass it through water. And I acquired a loincloth according to the word of the Lord and put it around my loins. And the word of the Lord came to me, saying: Take the loincloth that is around your loins, and arise and go to the Euphrates, and hide it there in the cleft of the rock." After some days he comes there, and finds this loincloth rotted through. And the Lord adds to it, giving the occasion for the interpretation of the loincloth, saying: "Just as the loincloth clings to the loins of a man, so did I cause the house of Israel and the whole house of Judah to cling to myself, says the Lord, that they might become for me a renowned people and a boast and a glory, and they did not listen to me." Therefore the prophet is taken up in the place of God, girding around his loins the linen loincloth, as God girds the people; for "I caused to cling to myself," he says, "this people," meaning that the people, as it were, becomes God's loincloth. But why does the people become God's loincloth around his loins? Let him who is able, reading Ezekiel and beholding God, as it were, given a bodily form by the word — and in what manner the parts of him from the loins downward are fire, but the parts from the loins upward are amber — let him search out the word, why the lower part of God is fire. The things from the loins and from generation, these are fire. For all things that are in generation have need of the purification that comes from fire, all things in generation have need of chastisement. But the things above the loins and beyond generation, these are matter as in its purest and most precious state; for amber is said to be more precious than gold. […]

(Chapter 13, verse 1 onwards) Thus says the Lord to me: Go and acquire for yourself a linen loincloth (or belt) and put it on your loins, and do not bring it into water (or do not pass it through water). So I acquired a loincloth according to the word of the Lord and put it around my loins. Then the word of the Lord came to me a second time, saying: Take the loincloth (or belt) that you acquired, which is around your loins, and go to the Euphrates and hide it there in a hole in the rock. And I went and hid it in the Euphrates, as the Lord had commanded me. And after many days, the Lord said to me: Arise and go to the Euphrates, and take from there the girdle (or belt) that I commanded you to hide there. And I went to the Euphrates, and dug, and took the girdle from the place where I had hidden it, and behold, the girdle had decayed so that it was of no use. And the word of the Lord came to me, saying: Thus says the Lord: So will I cause the pride (or injury) of Judah and the great pride of Jerusalem and this evil people, who refuse to hear my words and walk in the stubbornness (or direction) of their evil hearts: they have gone after foreign gods to serve them and worship them, and they will be like this useless girdle. For as the waist is joined to the loins of a man, so have I joined to me all the house of Israel, and all the house of Juda, saith the Lord: that they might be my people, and for a name, and for a praise, and for a glory: but they would not hear. The girdle, or waistband, which is joined to the loins, is the people of Israel: they who have been taken up from the earth, and have not been softened, nor made white, and yet they have cleaved to God through his mercy. […]

Furthermore, this Paul said strongly that "the kingdom of God is not a matter of eating and drinking"—or abstinence from wine or meat—"but of righteousness, peace and joy in the Holy Spirit." Which of them goes around like Elijah wearing a sheepskin and a leather belt? Which of them wears no shoes and nothing but a piece of sackcloth like Isaiah? Or with nothing on but a linen loincloth, like Jeremiah?

The girdle, or loincloth, which is attached to the loins of God, is the people of Israel, who, like this piece of linen, were assumed from the earth unwashed and having no softness or beauty, yet were nevertheless joined to God through his mercy. When Israel sinned (which is why it was represented as a loincloth), it was led across the Euphrates and Assyria and there hidden, that is, absorbed, in a manner of speaking, into the crowd of larger and innumerable peoples and from captivity. Despite this, they did not observe the precepts of God after they were restored but went after other gods in the extreme, even raising their hand against the Son of God, and then they wasted away in everlasting perdition. God's loincloth is also every holy person who is assumed from the earth, even from the dust of the earth, and united to God as a companion, who, in a certain way, surrounds and covers with greater diligence the things that appear in God's church to be indecent, lest they become vulnerable to the stings of the pagans and heretics. Yet, as the loincloth was affected by the water of the Euphrates and was assimilated to the river's flow, so also Israel was imbued with the atmosphere of the Assyrian region, which destroyed its original strength and corrupted and dissolved it. Even though Israel returned to God's service, it was never able to regain its pristine beauty, though this was not due to any severity of God's part, but only to the Israelites' own wickedness, for they would not hear his word but did whatever seemed good to themselves and walked in the depravity of their own hearts. […]