How is it free will when God said He would give people a new heart?

Answer:

"Thus says the LORD, the God of Israel: 'Like these good figs, so will I acknowledge those who are carried away captive from Judah, whom I have sent out of this place for their own good, into the land of the Chaldeans. For I will set My eyes on them for good, and I will bring them back to this land; I will build them and not pull them down, and I will plant them and not pluck them up. Then I will give them a heart to know Me, that I am the LORD; and they shall be My people, and I will be their God, for they shall return to Me with their whole heart. And as the bad figs which cannot be eaten, they are so bad' -- surely thus says the LORD -- 'so will I give up Zedekiah the king of Judah, his princes, the residue of Jerusalem who remain in this land, and those who dwell in the land of Egypt. I will deliver them to trouble into all the kingdoms of the earth, for their harm, to be a reproach and a byword, a taunt and a curse, in all places where I shall drive them. 'And I will send the sword, the famine, and the pestilence among them, till they are consumed from the land that I gave to them and their fathers'" (Jeremiah 24:5-10).

God is explaining to the captives in Babylon that everything isn't quite as it appears. When Nebuchadneezar conquered Judah, he did it in three phases. This statement is written between the second and third phases. Those who had been carted off to Babylon thought they were in a horrible position, despised by God and rejected because they were ripped away from their homeland. What God is saying is that they are in a better position. He has moved out those whom He thinks are salvageable. Those who remained in Judah are those who are so bad that God doesn't see being able to save them.

This is a generalization, not an exact accounting. You must remember that Jeremiah is among those left in Judah and Ezekiel, who is Babylon, makes it clear that there are bad elements among the captives in Babylon. Still, the overall statements are true.

What God is saying is through the punishment of Judah, He would shake the people out of their complacent idolatry. After centuries of Israelites trying to play both sides, they will finally turn to the Lord completely. It is exactly what God promised in the days of Moses: "And the LORD your God will circumcise your heart and the heart of your descendants, to love the LORD your God with all your heart and with all your soul, that you may live" (Deuteronomy 30:6). Some people just don't learn except on through hard-knocks.

"And I will sanctify My great name, which has been profaned among the nations, which you have profaned in their midst; and the nations shall know that I am the LORD," says the Lord GOD, "when I am hallowed in you before their eyes. For I will take you from among the nations, gather you out of all countries, and bring you into your own land. Then I will sprinkle clean water on you, and you shall be clean; I will cleanse you from all your filthiness and from all your idols. I will give you a new heart and put a new spirit within you; I will take the heart of stone out of your flesh and give you a heart of flesh. I will put My Spirit within you and cause you to walk in My statutes, and you will keep My judgments and do them. Then you shall dwell in the land that I gave to your fathers; you shall be My people, and I will be your God. I will deliver you from all your uncleannesses. I will call for the grain and multiply it, and bring no famine upon you. And I will multiply the fruit of your trees and the increase of your fields, so that you need never again bear the reproach of famine among the nations. Then you will remember your evil ways and your deeds that were not good; and you will loathe yourselves in your own sight, for your iniquities and your abominations. Not for your sake do I do this," says the Lord GOD, "let it be known to you. Be ashamed and confounded for your own ways, O house of Israel!" (Ezekiel 36:23-32).

Here God promises to restore Israel after they have been purged from the sins through the trials God sent them. Again, this is as God had promised: "When the Lord has washed away the filth of the daughters of Zion, and purged the blood of Jerusalem from her midst, by the spirit of judgment and by the spirit of burning, then the LORD will create above every dwelling place of Mount Zion, and above her assemblies, a cloud and smoke by day and the shining of a flaming fire by night. For over all the glory there will be a covering" (Isaiah 4:4-5). Israel would not turn from her sins any other way, so God used the severe trial of captivity and destruction to get Israel to finally accept the reality of her sins. And after that cleansing would come pardon. "I will cleanse them from all their iniquity by which they have sinned against Me, and I will pardon all their iniquities by which they have sinned and by which they have transgressed against Me" (Jeremiah 33:8).

Again we are not talking about each individual but the overall trend of the entire nation.

You are right, not everyone changes, but a lot of people can learn lessons. Free will is still there. Individually, not everyone turned. For example, when Israel was allowed to return, only a small portion returned. Many put down roots in Babylon and never returned to their nation or their God, but that too was a part of the weeding out process.