Christianity is not a school of ideas or a collection of beautiful temples and lovely art; it is a living people who follow Jesus and give witness to him every day, Pope Francis said.
"Am I a Christian giving witness to Jesus or am I a simple numerary of this sect," unable to let the Holy Spirit "drive me forward in my Christian vocation?" he asked in his homily at Mass Tuesday in the Domus Sanctae Marthae, where he lives.
"A Christian who doesn't give witness is unfathomable," he said, according to a report by Vatican Radio.
"We are not a religion of ideas, of pure theology, of beautiful things and commandments.
"No, we are a people who follow Jesus Christ and give witness -- that is, want to give witness to Jesus Christ -- and this witness sometimes ends up being giving one's life," he said.
In his homily, the pope looked at the martyrdom of St. Stephen, the first martyr of the church. Like Jesus, the saint was the object of jealous leaders who wanted to eliminate him and the target of false witnesses, the pope said.
But St. Stephen knew his accusers were resisting the Holy Spirit and he died, like Jesus, asking his persecutors be forgiven.
Those responsible for the martyr's death were filled with hate -- a hate that had been sown in their hearts by the devil, the pope said.
That is why, in one of the beatitudes, Jesus said, "blessed are you when they insult you and persecute you and utter every kind of evil against you falsely because of me."
Being persecuted, becoming a martyr, giving one's life for Jesus are all reasons to rejoice because "the blood of martyrs is the seed of Christians," he said.
"The devil can't stand seeing the holiness of the church or the holiness of a person without trying to cause some kind of trouble," he said.
Giving witness always bears fruit, he said, whether it is just one's daily witness to Christ, witness during very difficult times, during persecution or witness that ends with death.
"The church bears fruit and is a mother when it gives witness to Jesus Christ."
The church becomes sterile when it closes up inside itself, when "it believes itself to be, let's say, a 'school of religion' with lots of beautiful ideas, with many beautiful temples, with many fine museums, with many gorgeous things."
Christians who don't give to others the new life they've been given by Christ remain "sterile," he said.
But people need the help of the Holy Spirit, especially in difficult moments, when faced with hard choices or when tempted by the many things "we have to say, 'no' to," he said.
Pray to the Holy Spirit who "makes us strong in order to take the path of witness."