What a contrast!
Philip, on going forth from Jerusalem, was intent on leading people to Jesus. Paul, on the other hand, went out from Jerusalem to torture, maim and kill as many Christians as he could find.
The blind rage fomenting in Paul's "boiler" was a power God wanted to turn for His use. Since Saul's passion was fueled by a love for God and His word, all God had to do was convince Him that Jesus really was the promised and predicted Christ; then all that zeal would be refocused on leading people to Jesus, too. He might even become one who would "labor more abudantly" than all the others!
Truth mattered to Saul; it always did. So, when he was presented with overwhelming evidence he became as passionate for Jesus as he had been adamant against Him. The resultant body of work—churches and literature—stands as historic evidence that God can and will change lives.