In Jeremiah 13:8–11 the Lord explains to Jeremiah the meaning of the symbolic act he has instructed his prophet to complete in Jeremiah 13:1–7. It should be noted, first, that the people of Judah shall be like this loincloth, which is good for nothing
because they are an evil people, who refuse to hear my words, who stubbornly follow their own heart and have gone after other gods to serve them and worship them.
In the symbolic act the loincloth represents the people of Judah, and it is their stubborn disobedience and idolatry that has defiled the people and made them useless to the Lord as his covenant people.
10 This evil people, who refuse to hear my words, who stubbornly follow their own heart and have gone after other gods to serve them and worship them, shall be like this loincloth, which is good for nothing.