Often times, we buy things because we heard by word of mouth that it is good. For example why do a lot of people have an iphone? It's often because someone you know has one, and you have heard how much they like it or you have used theirs, but mostly it's because of word of mouth.
Not only that, most people eat at places that other people have told them to try because it's so good. There are even websites like yelp and others that put restaurants in order form word of mouth and rating as to how good they are from a consensus of people.
In Acts 13:13-52 that 's exactly what Paul did about our faith and Savior Jesus Christ. He reviews it all. He told others the "Good News". He didn't go about by his testimony because he has an awesome one, he didn't go about by trying to friend all those people individually, no he spoke the truth to a multitude of people right there. He basically shared his excitement for Christ.
Paul wasn't some lunatic on the street speaking, he was educated, maybe even well thought of as we study his place in society and his status pre-salvation. So maybe that 's why people listened but we know it was God, we know that Paul was intimate with God and with the Savior that he knew what he was speaking of and was empowered by the Holy Spirit to say all he did.
God did the work there and the very next week, the whole city showed up to hear.
So what are we doing? Are we sharing our excitement for Christ and the "good news" are we so intimate with God that he spills out of us and his glow overcomes our very being?