How do we know God's grace is necessary for understanding the gospel?

The necessity of God's grace is underscored in the sermon as it points out that, until God acts through His Spirit, all men remain in a state of spiritual blindness. In Acts, we see the apostles' preaching elicited two fundamentally different responses among the listeners—those who were able to perceive the gospel's significance did so because of God's grace acting upon their hearts, whereas those who mocked did not experience this divinely enabled perception. 1 Thessalonians 1:5 further affirms that the gospel comes in power and in the Holy Spirit, demonstrating that a transformed heart is a result of God’s initiative. The importance of this divine intervention in the hearts of men cannot be overstated; it is solely by God's grace that people are able to turn from spiritual blindness to the light of the gospel.