How do we know that God opens hearts to believe?

In Acts 16:14, we read about Lydia, a seller of purple, whose heart the Lord opened to heed the preaching of Paul. This account highlights that the ability to understand and accept spiritual truths comes from God’s work in our hearts. It is not a mere act of human will but a divine operation. God's initiative in opening hearts is essential to our understanding of salvation, as evidenced in other scripture, such as Ephesians 1:4-5, which speaks of God's electing grace from before the foundation of the world. Without His action, no one could come to faith.