Every nation has the right to distinguish, by country of origin, who can migrate to it and apply appropriate immigration policies, according to the great medieval scholar and saint Thomas Aquinas.

In a surprisingly contemporary passage of his Summa Theologica, Aquinas noted that the Jewish people of Old Testament times did not admit visitors from all nations equally, since those peoples closer to them were more quickly integrated into the population than those who were not as close.

Some antagonistic peoples were not admitted at all into Israel due to their hostility toward the Jewish people.

The Law “prescribed in respect of certain nations that had close relations with the Jews,” the scholar noted, such as the Egyptians and the Idumeans, “that they should be admitted to the fellowship of the people after the third generation.”

Citizens of other nations “with whom their relations had been hostile,” such as the Ammonites and Moabites, “were never to be admitted to citizenship.”

“The Amalekites, who were yet more hostile to them, and had no fellowship of kindred with them, were to be held as foes in perpetuity,” Aquinas observed.

For the scholar, it seemed sensible to treat nations differently, depending on the affinity of their cultures with that of Israel as well as their historic relations with the Jewish people.

In his remarkably nuanced commentary, Aquinas also distinguished among three types of immigrants in the Israel of the Old Testament.

First were “the foreigners who passed through their land as travelers,” much like modern day visitors with a travel visa.

Second were those who “came to dwell in their land as newcomers,” seemingly corresponding to resident aliens, perhaps with a green card, living in the land but not with the full benefits of citizenship.

A third case involved those foreigners who wished “to be admitted entirely to their fellowship and mode of worship.” Even here, dealing with those who wished to integrate fully into the life and worship of Israel required a certain order, Aquinas observed. “For they were not at once admitted to citizenship: just as it was law with some nations that no one was deemed a citizen except after two or three generations.”

“The reason for this was that if foreigners were allowed to meddle with the affairs of a nation as soon as they settled down in its midst,” Aquinas logically reasoned, “many dangers might occur, since the foreigners not yet having the common good firmly at heart might attempt something hurtful to the people.”

In other words, Aquinas taught that total integration of immigrants into the life, language, customs and culture (including worship, in this case) was necessary for full citizenship.

It requires time for someone to learn which issues affect the nation and to make them their own, Aquinas argued. Those who know the history of their nation and have lived in it, working for the common good, are best suited to participate in decision-making about its future.

It would be dangerous and unjust to place the future of a nation in the hands of recent arrivals who do not fully understand the needs and concerns of their adoptive home.

When facing contemporary problems, modern policy makers can often benefit from the wisdom of the great saints and scholars who have dealt with versions of the same issues in ages past.

Aquinas’ reflections reveal that similar problems have existed for centuries—indeed, millennia—and that distinguishing prudently between nations and cultures doesn’t automatically imply prejudice or unfair discrimination.

Sometimes, it’s just the right thing to do.

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