Jeremiah 13:11 English Standard Version
For as the loincloth clings to the waist of a man, so I made the whole house of Israel and the whole house of Judah cling to me, declares the LORD, that they might be for me a people, a name, a praise, and a glory, but they would not listen.
What is the significance of this loincloth image?
The operative word, אֵזוֹר (ezor), translated "loincloth" (ESV) is used to decribe several things such as:
In either case the point of the metaphor in the enacted parable of Jer 13 is clear - God regarded Israel as a waistband/loincloth for several reasons:
Indeed, this was the sated purpose of the chosen nation of Israel:
Ex 19:5, 6 - Now if you will indeed obey My voice and keep My covenant, you will be My treasured possession out of all the nations—for the whole earth is Mine. And unto Me you shall be a kingdom of priests and a holy nation.’
1 Peter 2:9, 12 - But you are a chosen people, a royal priesthood, a holy nation, a people for God’s own possession, to proclaim the virtues of Him who called you out of darkness into His marvelous light. ... Conduct yourselves with such honor among the Gentiles that, though they slander you as evildoers, they may see your good deeds and glorify God on the day He visits us.
Benson reaches a similar conclusion:
Jeremiah 13:11. For as the girdle cleaveth to the loins of a man — Here God shows the prophet why he commanded him to put the girdle about his loins. So have I caused — Rather, had I caused; to cleave unto me the house of Israel — I had betrothed them to myself in righteousness, and entered into a marriage covenant with them, that they might cleave to me as a wife cleaveth to her husband. By the laws I gave them, the prophets I sent among them, and the favours which, in my providence, I showed them, I brought them near to myself, and allowed them access to me, and intercourse with me, above every other nation. That they might be unto me for a people — A peculiar people; that they might have the honour of being called by my name; and for a praise and a glory — That I might be glorified by their showing forth my power, goodness, and faithfulness, and all my other glorious perfections to the world, so that I might be honoured and praised through them.
The loincloth signifies "the whole house of Israel and the whole house of Judah". It signifies this in that they were supposed to cling as tightly to God as a loincloth clings to a man; as the verse you quote states.
It is marred to signify how the they were marred and good for nothing (verse 10). It is a somewhat unpleasant image similar to shock of the potter's vessel breaking in Jeremiah 19, or the dung in Ezekiel 4.
The marring represents the way Judah's pride will be marred (verse 9). However, the fact that it was linen - so with a certain value - and that God ordered and enacted it's instructions helps to illustrate God's seriousness in threatening to destroy the people of the land which he threatens a few verses later in verse 14.
The imagary here is talking about the relationship Israel and Jehovah God. Note two different ways this is seen:
"Hips" from Insight on the Scriptures
Jehovah spoke of the houses of Israel and Judah as having been like a belt [or loincloth] on his hips, so closely had he held them to himself, in order that they might become to him a praise and something beautiful. [my addition]
Matthew Henry's Concise Commentary
The people of Israel had been to God as this girdle. He caused them to cleave to him by the law he gave them, the prophets he sent among them, and the favours he showed them.
