How do we know that God opens the hearts of sinners?

Acts 16 illustrates God's sovereignty in salvation, as the Lord opened Lydia's heart to respond to Paul's preaching. This event underscores that salvation is initiated by God, who must open hearts to hear and accept the gospel. The sermon emphasizes that both the opportunity to preach and the response from the listeners are entirely dependent on God's action. This means that without God's intervention, individuals remain spiritually dead and incapable of responding positively to the gospel message.