VATICAN CITY -- Pope Francis advised future priests and nuns Saturday to shun costly trappings such as the latest smartphones or fast cars so they can use more resources to help the poor.

In an off-the-cuff lecture to a Vatican auditorium full of seminarians and novices, and to thunderous applause, Francis urged them to keep "freshness" and "joy" in their lives.

He took to task those in their ranks who "are too serious, too sad."

"Something's not right here," Francis told his rapt audience. "There is no sadness in holiness," said Francis, adding that such clergy lack "the joy of the Lord."

He cautioned the future priests and nuns that he wasn't talking about superficial joy -- "the thrill of a moment doesn't really make us happy." Francis warned his audience against seeking "the joy of the world, the latest smartphone, the fastest car."

"It hurts my heart when I see a priest with the latest model car," Francis said, then joked that his audience will think 'now we have to go by bicycle.' "

"Cars are necessary. But take a more humble one," said Francis. He said the seminarians and novices should "think of how many children die of hunger" and dedicate the savings to them.

While there have been calls within the church for the Vatican to ease the requirement for celibacy for priests, nuns and brothers, Francis praised chastity.

"We are victims of a culture of the 'temporary,' " Francis said, adding that celibacy vows for those becoming priests or nuns should be a "definitive choice."

The Vatican allows married clergy in strictly limited cases: married men in the Eastern rite church can be ordained priests, and married Anglican clergy who later convert can stay married after joining the Catholic Church.

During his remarks, Francis praised Mother Teresa, the late nun who cared for the most impoverished sick of Calcutta, India, and held her up as a courageous example. "I would like a more missionary church," the pope told the young people, who seemed to hang on his every word. "Not so much a tranquil church, but a beautiful church that goes forward."

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