How Does This Great Change Happen?

Who Does What?

First God calls people to Himself, enabling them to hear and understand the gospel.

We preach Christ crucified, to the Jews a stumbling block and to Gentiles foolishness, but to those who are the called, both Jews and Greeks, Christ the power of God and the wisdom of God (1Cor 1:23-24). The only reason anyone thinks the Cross is anything other than foolishness is the call of God.
Everyone who calls on the name of the Lord will be saved; for on Mount Zion and in Jerusalem there will be deliverance, as the Lord has said, among the survivors whom the Lord calls (Joel 2:32). The only people who call on God are those God has already called to Himself.

Then He graciously grants those He calls the free gifts of repentance and belief.

with gentleness correcting those who are in opposition, if perhaps God may grant them repentance leading to the knowledge of the truth (2Tim 2:25).
When they heard this, they quieted down and glorified God, saying, "Well then, God has granted to the Gentiles also the repentance that leads to life" (Acts 11:18; cf. also John 15:16; Acts 2:39; 16:14; 1John 4:10).
Conversion is therefore that work of God in us whereby He sovereignly grants life to our spiritually dead hearts and produces in us a willingness to repent of our sins and believe in the gospel.