The Day of the Pentecost and Lydia

Do you know that the Holy Spirit is God? God the Holy Spirit will always be with us. The Holy Spirit is our helper. He came to the disciples on the day of Pentecost. By the power of the Holy Spirit, the disciples were able to teach Lydia and others. Lydia accepted to be baptized. Through the Holy Spirit, we now know about God.
Why did God send us the Holy Spirit?
What made Lydia to believe in God?