He recounted his encounter with a man engaged to be married who was looking for a church that would complement his fiancée's dress and would not be far from a restaurant.
"It's social issue, and how do we change this? I don't know," the Pope said.
He noted that as Archbishop of Buenos Aires he had prohibited marriages in the case of "shotgun weddings" where the prospective bride was pregnant. He did this on the grounds there was a question of the spouses' free consent to marry.
"Maybe they love each other, and I've seen there are beautiful cases where, after two or three years they got married," he said. "And I saw them entering the church, father, mother and child in hand. But they knew well (what) they did."
Pope Francis attributed the marriage crisis to people who "don't know what the sacrament is" and don't know "the beauty of the sacrament."
"They don't know that it's indissoluble, they don't know that it's for your entire life. It's hard," the Pope said.
He added that a majority of couples attending marriage prep courses in Argentina typically cohabitated.
"They prefer to cohabitate, and this is a challenge, a task. Not to ask 'why don't you marry?' No, to accompany, to wait, and to help them to mature, help fidelity to mature."
He said that in Argentina's northeast countryside, couples have a child and live together. They have a civil wedding when the child goes to school, and when they become grandparents they "get married religiously."
"It's a superstition, because marriage frightens the husband. It's a superstition we have to overcome," the Pope said. "I've seen a lot of fidelity in these cohabitations, and I am sure that this is a real marriage, they have the grace of a real marriage because of their fidelity, but there are local superstitions, etc."
"Marriage is the most difficult area of pastoral work," he said.
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