Who opened Lydia's heart so she responded to the gospel?
God opened Lydia's heart so that she responded to the gospel. Scripture indicates it was not Lydia herself and not Paul who opened it, but God did. This illustrates that God is the seeker and brings a person to the place of believing, rather than man seeking God by his own desire.
Les explains that man in his own desire will never seek God; God is the seeker, and believers should not give themselves credit for having found salvation. Instead, God found them and brought them to the place where they believe. He points to Lydia as the example: it was God who opened her heart, not her, and it was not Paul who opened it, but God did.