Paul was the greatest evangelist of all time. Billy Graham is likely a close second, but Paul was not a Billy Graham. Paul would travel from city to city leading thousands to Jesus, but then along the way he would stop for a few months in one city to help the new converts grow.
So many times we think that leading people to Jesus we have done sufficiently. I do not follow the "once saved always saved" philosophy (though I do believe in eternal security, but that's based on God's faithfulness to us, not the other way around); hence, people need to remain in Jesus and grow in Him. That's why Paul stayed.
It's the reason my calling has always been to the church, not to evangelism. I'm not saying I haven't been called to witness to others, because that's the calling that's universal to all Christians. But my personal focus is on helping already saved people to grow in Christ consistently, and the church is the perfect outlet to help them know Christ and know about Christ better.
So remember, your walk with the Lord is only as strong as what you put into it. Get into the habit of reading your Bible and praying every day, and watch your ritual religion become something more like the relationship people say it is.