Why was Saul of Tarsus infuriated when he heard about Jews following Jesus of Nazareth?
Saul of Tarsus was infuriated because he was a Pharisee defending his religion. Hearing that more Jews were following Jesus of Nazareth as the Messiah, and hearing reports of His miracles, threatened the religious system he was committed to uphold, so each report provoked fierce opposition.
Les explains that Saul of Tarsus was a Pharisee of the Pharisees and one of the key men of the Sanhedrin. He was likely in his thirties, almost the same age as Jesus. As Saul heard about the miracles Jesus of Nazareth was performing, and every time he heard that more Jews were following after the Messiah from Nazareth, it totally infuriated him. The reason was that he was defending his religion. Later, Les notes, he also had to defend his apostleship, so he had a lifetime of fighting.