MUNICH, Germany — Pope Benedict XVI yesterday warned modern societies to be wary of allowing faith in science and technology to make them deaf to God’s message, and he suggested that Asia and Africa could teach the wealthier West something about faith.

In his sermon to some 250,000 pilgrims at an open-air Mass in Munich, Benedict said modern people suffered from “hardness of hearing” when it comes to God.

“Put simply, we are no longer able to hear God — there are too many different frequencies filling our ears,” he said. “What is said about God strikes us as prescientific, no longer suited to our age.”

“People in Asia and Africa admire our scientific and technical progress, but, at the same time, they are frightened by a form of rationality, which totally excludes God from man’s vision, as if this were the highest form of reason.”

Benedict, on the second day of a six-day homecoming trip to his native Bavaria, rode in his popemobile through a cheering crowd to say Mass atop a platform in a sprawling field on the outskirts of Munich, where he served as archbishop between 1977 and 1982.

People waved yellow and white Vatican flags and blue and white Bavarian ones, while Mexican, Croatian, Slovak, and Polish banners also fluttered above the crowd.

The need for Western Europe to return to its Christian roots is one of Benedict’s favorite themes, and he is repeating it during his visit to his native country — home to a shrinking and liberal Catholic Church and a highly secularized society.