On the campaign trail and in Congress, Senator Bernie Sanders has frequently invoked Pope Francis, quoting his writings about the “idolatry of money,” sending solicitations for donations headlined “Why we must listen to Pope Francis” and praising the pope as a “radical” for “speaking out with courage and brilliance about some of the most important issues facing our world.”

Someone was listening. On Friday, Mr. Sanders was scheduled to fly to Rome to address the Pontifical Academy of Social Sciences, in effect the Vatican’s in-house think tank on social, economic and environmental issues.

“We invited the candidate who cites the pope the most in his campaign, and that is Senator Bernie Sanders,” said Bishop Marcelo Sánchez Sorondo, the academy’s chancellor.

Monsignor Sánchez Sorondo, an Argentine who is close to the pope, said that Mr. Sanders’s focus on climate change and his attention to poor people on the margins of society were “very analogous to that of the pope.” He said that made the Vermont senator an obvious person to invite to Friday’s conference, which celebrates the 25th anniversary of an encyclical by Pope John Paul II about the potential pitfalls of the market economy after the fall of the Berlin Wall.