Paul was a follower of Jesus who loved Jesus and wanted everyone to know about Him. He traveled to many cities, helped start churches, and wrote letters like the book of Romans to encourage other followers of Jesus. 

But, Paul wasn't always a follower of Jesus himself. Before Paul knew Jesus, we know him as Saul (Saul was his Hebrew name and Paul was his Roman name). In Acts chapter 9, we learn that Saul knew the Old Testament, but he didn't believe Jesus was the Son of God. He actually tried to stop people from following Jesus, and even hurt them because of their faith.

But one day, Saul was traveling to Damascus and Jesus met Saul and completely changed his heart. Saul was now on a mission to spread the Good News of Jesus near and far because he wanted people to know that God's love is for everyone. We see this in John 3:16:

For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.