When the Jerusalem council took up the question of Gentiles coming to faith in Jesus Christ, it was God “who knows the heart, bore witness to them, by giving them the Holy Spirit just as He did to us, and he made no distinction between us and them, having cleansed their hearts by faith.” (15:8–9). Only God can cleanse the heart by faith and give the Holy Spirit.
In the same way, when Paul and Timothy met Lydia, they recognized that “the Lord opened her heart to pay attention to what was said by Paul” (16:15). No programs, methods, or gimmicks can accomplish the work of God. This forces us to depend on the Holy Spirit to work in those we present the gospel and God’s Word to. The more we realize this the more dependent we will become, and the more we will see God work as a witness to the power of the gospel.