Very slowly, the church under the guidance of Pope Francis is facing the fact that many Catholic couples cohabit before marriage, use contraception freely and divorce and remarry without seeking an annulment, says the BBC's David Willey in Rome.
He said in his homily that families are "bricks that build society", but also believes that the church should forgive those who have sex outside marriage or who don't obey church teaching to the letter.
It was the first marriage Pope Francis has conducted in his 18-month papacy. The last wedding to be presided over by a pope took place under John Paul II in 2000.