Acts 16:11-15
11 So, setting sail from Troas, we made a direct voyage to Samothrace, and the following day to Neapolis, 12 and from there to Philippi, which is a leading city of the district of Macedonia and a Roman colony. We remained in this city some days. 13 And on the Sabbath day we went outside the gate to the riverside, where we supposed there was a place of prayer, and we sat down and spoke to the women who had come together. 14 One who heard us was a woman named Lydia, from the city of Thyatira, a seller of purple goods, who was a worshiper of God. The Lord opened her heart to pay attention to what was said by Paul. 15 And after she was baptized, and her household as well, she urged us, saying, "If you have judged me to be faithful to the Lord, come to my house and stay." And she prevailed upon us.
ESV
Lydia was a worshiper of God. She was not a Jew but worshipped God with them. If the town did not have enough Jewish men to warrant a synagogue, it was customary to gather by water for worship and prayer on the Sabbath day. No men appear to be in the number gathered before Paul. Often women seem more able to hear the Spirit and more likely to respond.
Here we see the work of the Holy Spirit combined with the service of Paul. Paul spoke the words, but the Holy Spirit is the One Who beckons and works within the heart. We come into play as we plant the seed of the Word. That seed prospers based on the interaction of the Spirit and the individual. There can be no boasting on our part for the light we bring is His, not ours.
Paying attention is another way of saying “let those with ears hear”. True hearing leads to belief, which leads to walking with God. She did not merely agree with Paul, but acted on that belief. After her baptism, she opened her house to Paul and his companions. She had opened her heart after the Lord had knocked at her heart’s door. A heart that seeks God will find Him. We only have to pay attention.