God is going to remove his support and supply from his people. Food, protection, civil and religious leadership. God is going to let them suffer.
Why is He doing this? Because their speech and their deeds are against the Lord, defying his glorious presence (v8). They proclaim their sin, they are proud of it. They have oppressed others. They will be given what they deserve.
The people look impressive and are proud of that appearance, but God is going to remove the mask and show up their utter shame. Very strong language is used - the daughters of Zion who are currently "mincing" around will have their "secret parts laid bare". There will be rottenness instead of perfume, baldness instead of hair.
This is God's grace. Without this, they will continue as they are, without him. God is going to confront them with their natural state without Him - they need to see what that is really like in order that they can return to him. Having their whole world turned upside down is worth it if it results in a cry of desperation to God. God is too committed to their good to leave them in their sin.