Again, Jeremiah seems to insert his own voice into his prophecy of looming judgment, and he urges the people of Jerusalem to wash your hearts from evil.
This is a call for deep change. They are to remove the deeply ingrained dirt of moral and spiritual failure from their hearts (see Jeremiah 2:22). External religious reform is not enough (Mackay, p 222).1
14 O Jerusalem, wash your heart from evil, that you may be saved. How long shall your wicked thoughts lodge within you?