Like St. Paul, Christians must not only know Jesus with their heads but invite him into their hearts through a personal encounter with Christ, Pope Francis said.
"An encounter with the Lord is what changed a life," the pope said during his March 29 general audience in St. Peter's Square in which he reflected on St. Paul's conversion and praised him as a model of what it means to have a "passion for the Gospel."
St. Paul participated in the persecution of early Christians before converting and founding several Christian communities.
Pope Francis said that St. Paul's experience of Christ converted the saint's zeal for the Jewish law as a Pharisee into a zeal for the Gospel and changed him from someone determined to destroy the church into an apostle.
"Becoming Christian is not a type of makeup that alters your face," said the pope. "True change takes place in the heart, and that's what happened to Paul."
He explained that while studying the faith has its value, developing a passion for the Gospel like St. Paul had is "not a matter of understanding or study," but of lived experience.
"You can study all the theology you want. You can study the Bible, all that, and become atheist or worldly," he said. "Studying is important, but it doesn't generate a new life of grace."
Pope Francis warned against becoming a "refined Catholic" who, by focusing solely on following the church's commands, has developed an abstract idea of Jesus in their lives.
"If Jesus has not entered your life, it has not changed. You may be a Christian only externally," he said. "The real Christian is the one who receives Jesus internally, that changes his heart," he said.
Pope Francis then encouraged Christians to ask themselves: "What does Jesus mean to me?"
"Have I let him into my life? Or do I keep him at arm's length so that he does not come in? Have I let myself become changed by him? Or is Jesus just an idea, a theology?" asked the pope.
When a Christian truly makes Jesus a central part of their life, said the pope, "they feel the fire, like Paul, to preach Jesus, to talk about Jesus, to help people and do good things."
If one only has an abstract idea of Jesus, on the other hand, "they remain a theorist of Christianity," said the pope.