The reason why the girdle was chosen as the symbol. Similarly, Israel was the people chosen and set apart that in and by them the Holy Spirit might work for the salvation of mankind.
Related Commentaries of Jeremiah 13:11
Jeremiah 13:11
11 For as the girdle cleaveth to the loins of a man, so have I caused to cleave unto me the whole house of Israel and the whole house of Judah, saith the LORD; that they might be unto me for a people, and for a name, and for a praise, and for a glory: but they would not hear.