Never before has Pope Francis visited anyone in the United States. On Wednesday, Sept. 23, he will enter the White House. (Editor’s note: This column was written in advance of Pope Francis’ visit.)

His visit with President Obama is the first of a series of events planned for a five-day stay in this country. The two men have already met, in Rome, and their conversation promises to be cordial and mostly private.

The next day, in contrast, the world will be able to see Pope Francis arrive at the United States Capital to address a joint session of Congress, at the invitation of Speaker John Boehner. This very public speech, to a diverse and contentious group of legislators, will be the first and (to me) maybe the most interesting of those he will make next week.

On Friday, the pope will address the United Nations General Assembly — an even more diverse and contentious group — as three of his predecessors have already done.

Finally, the pope will encounter vast crowds in Philadelphia at the World Meeting of Families. This, unlike the two others, is an unmistakably Catholic occasion. It will be an opportunity to join in worship and perhaps also to listen for new perspectives on church teaching.

My special interest in the address to Congress comes in part from the fact that so many members are Catholics. That means almost a third of the House of Representatives and about a quarter of the Senate. Those watching the speech will see two Catholics sitting behind the pope: Speaker Boehner and Vice President Biden, the Senate president.

Presumably, some of these Catholic legislators take their religious affiliation more seriously than others. Even those who attend Mass weekly have their preferences among church teachings. Those who oppose abortion do not always oppose the death penalty, and vice versa.

I suspect that, for some, Pope Francis’ speech may be their first up-close discovery of how passionately their church cares about the earth. They will hear, in a much more immediate way, the message of Laudato si, the pope’s recent encyclical letter on our obligation to safeguard the earth, our common home.

Encyclicals, or public letters, have been used by modern popes to address important moral and social issues. Many pass unnoticed, except by specialists; this one has elicited praise from religious and secular readers alike. But how will our Catholic legislators respond?

At this stage in our history, I am confident that the officeholders will be polite.

However, some will surely take issue with the pope, despite all his charm. There are Republicans who will fear the pope is a Marxist. There are Democrats who will fear the economic effects of his message on their constituents.

Allow me to suggest, from the sidelines, that this event could make a difference in our society for which our children, and their children, will be forever grateful.