Jeremiah heard God well: Judah didn’t repent and Nebuchadnezzar invaded Judah, taking the first exiles from Jerusalem back with him to Babylon.
The King learned the power of God from two incidents: Daniel interpreting a dream and his three friends surviving a ‘fiery furnace’, as it’s often called.
After the dream, the King said:
Daniel 2:47 Truly, your God is the greatest of gods, the Lord over kings, a revealer of mysteries, for you have been able to reveal this secret.
And after seeing a fourth man, who looked like a god, in the furnace with the three men he’d thrown in there, the King said:
Daniel 3:28 Praise to the God of Shadrach, Meshach, and Abednego! He sent his angel to rescue his servants who trusted in him. They defied the king’s command and were willing to die rather than serve or worship any god except their own God. Therefore, I make this decree: If any people, whatever their race or nation or language, speak a word against the God of Shadrach, Meshach, and Abednego, they will be torn limb from limb, and their houses will be turned into heaps of rubble. There is no other god who can rescue like this!
He still hadn’t quite called God his own.