Pope Francis has once again weighed in on Europe’s migrant crisis, urging immigrants to respect local laws and customs while conserving their own cultural idiosyncrasies.

After his midday Angelus prayer on Sunday, the Pope told the crowd gathered in Saint Peter’s Square that the day was marked for the celebration of the World Day of Migrants and Refugees, and that this year’s commemoration would focus on “Underage Migrants, Vulnerable and Voiceless.”

“These little brothers and sisters of ours,” Francis said, “especially those who are unaccompanied, are exposed to numerous perils. I tell you there are many! It is imperative to adopt every possible measure to guarantee protection and defense to underage migrants, as well as their integration.”

Turning to the immigrants present of different ethnic origins, Francis wished them a peaceful existence in their new home, but also encouraged them to respect “local laws and customs” while at the same time holding on to the values of their home cultures.

On other occasions, Pope Francis has insisted that the rule of law be applied faithfully when dealing with immigration issues.

The Pope’s words echoed an important passage from the Catholic Catechism, which does not endorse an open borders approach to immigration, but teaches that migration must take place within the rule of law.

The Catechism states that lawmakers may make the exercise of the right to immigrate “subject to various juridical conditions,” especially with regard to the immigrants’ duties toward their country of adoption.

“Immigrants are obliged to respect with gratitude the material and spiritual heritage of the country that receives them,” the text continues, “to obey its laws and to assist in carrying civic burdens.”

“The encounter of different cultures is always a source of mutual enrichment!” Francis said Sunday, before thanking the Migrant Office of the Diocese of Rome and all those who work with immigrants to “welcome and accompany them in their difficulties.” The Pope futher encouraged them to continue their efforts, remembering the example of Saint Frances Xavier Cabrini, the patron of migrants, whose 100th anniversary will be celebrated this year.

“This brave sister devoted her life to bringing the love of Christ to all those who were far from their homeland and families,” he said. “May her witness help us to take responsibility for our foreign brothers and sisters, in whom Jesus is present, often suffering, rejected and humiliated.”

“How many times in the Bible the Lord asked us to welcome migrants and foreigners, reminding us that we, too, are foreigners!” he said.

Pope Francis has been a vocal advocate of openness to migrants and refugees, while also cautioning nations not to take in more migrants than can be reasonably assimilated into society.

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