Jeremiah 19

“Then you shall break the flask in the sight of the men who go with you, 11 and say to them, ‘Thus says the Lord of hosts: “Even so I will break this people and this city, as one breaks a potter’s vessel, which cannot be made whole again; and they shall bury them in Tophet till there is no place to bury. vv.10-11

Read chapter 19
After reading about the potter and the clay in the last chapter where the clay was formable by the potter, we now have the flip side.  This flask has been baked and harden in the fire; there's no remolding of it, all that can be done now is to break it.   Once broken can never be pieced together again.  So the image God is using with the house of Judah.  Jeremiah was to proclaim both to the leaders and to the people this message of destruction that was going to break them.  The Babylonians were going to invade and destroy them, the majority would be killed and few would be taken into exile.  The land they had filled with their slain sacrifices to idols, valley of Tophet, would soon be overflowing with the dead from the slaughter by the Babylonians.
Sometimes someone has become so hard against God, that it takes to their breaking to see if they will ever seek the Lord.  As Jesus says, "Everyone who falls on that stone [Jesus] will be broken to pieces; anyone on whom it falls will be crushed." No man can repair a shattered vessel, yet it's material can be made into something new, as God will restore the whole house of Israel to a people again.
Have you been broken by the Lord and been made new?  Pray for those you know that are hardened toward God that they would be broken but not crushed.