Paul was a powerful advocate for Christ. In his letters, he helped the early Christians Jew and Gentile understand their relationship to Christ. His writings still help us to understand that as sin multiplies, so does grace.
So, how does one get called out of a murderous rampage into one the most effective evangelists the world has ever seen? It's called opportunity and preparation meeting a "calling". God created Paul for what he was going to ask him to do.
But why Paul? If you are like me, sometimes how God calls others out of their sinful lifestyle to be His missionaries, ministers and lay leaders while leaving you behind. You are sure that you could be used as well as anyone else and feel God may be ignoring your willingness to serve.
In Paul's case, he was perfect for God's use, he just didn't understand. Paul was a Jewish leader, lawyer, Roman, and Jew among many things. He knew God's law, Roman law, and was very well educated. He just didn't know Jesus.
As soon as Jesus revealed Himself, Paul believed. The same zeal he used to lock up Christians, he now used to free sinners. Paul knew Jesus and he realized grace.
What did God make you for? How is he using you? If you don't know, make it a point to study his word, pray and ask Him how you can serve.