WASHINGTON — Standing before a rapt Congress, Pope Francis issued a ringing call to action on behalf of immigrants Thursday, urging lawmakers to embrace “the stranger in our midst” as he became the first pontiff in history to address a joint meeting of the legislators.

Referencing the migration crisis in Europe as well as the United States’ own struggle with immigration from Latin America, Francis summoned lawmakers “to respond in a way which is always humane, just and fraternal.”

“We must not be taken aback by their numbers, but rather view them as persons, seeing their faces and listening to their stories, trying to respond as best as we can to their situation,” Francis urged.

He was welcomed enthusiastically to a House chamber packed with Supreme Court justices, Cabinet officials, and lawmakers of both parties, uniting the bickering factions before he even opened his mouth as all stood to cheer his arrival. The sergeant at arms intoned “Mr. Speaker, the pope of the Holy See,” and Francis made his way up the center aisle in his white robes, moving slowly as lawmakers applauded, some inclining their heads in bows.

After the speech, he appeared on a Capitol balcony and briefly addressed a cheering crowd of thousands below on the lawn and the Mall beyond. “Buenos dias,” he called out, and the crowd thundered its response. “God bless America!” he concluded, as he had in the House chamber.

Thursday’s speech was the latest highlight for the pope’s whirlwind three-day visit to Washington, the first stop on a three-city U.S. tour.

On Wednesday he was cheered by jubilant crowds as he visited the White House — where he and President Barack Obama embraced each other’s warnings on climate change — paraded through Washington streets in his “popemobile,” addressed U.S. bishops, noting the clergy sex abuse scandal, and celebrated a Mass of Canonization for Junipero Serra, the Spanish friar who founded major California missions.

Late Thursday, he moves on to New York and then later in the week to Philadelphia.

Introducing himself at the Capitol as “a son of this great continent,” the Argentine pope, reading his remarks slowly in English, spoke from the same dais where presidents deliver their State of the Union speeches. Behind him sat Vice President Joe Biden and House Speaker John Boehner, the first and second in line to the presidency, both Catholics. Outside, tens of thousands watched on giant screens, and many more were watching on TV around the world.