The saints saw the town as a place where Christians could fulfill their vocation to build a society marked by peace through the practice of justice, he said.

"Today there is a particular need for the church's service to the world to be expressed through enlightened lay faithful," involved in civil society "with a desire to serve that goes beyond their private interests and beyond partisan views," he said.

"The common good counts more than the good of the individual, and it's up to Christians to contribute to the birth of new public ethics," the Pope said.

The challenge facing the people of Sansepolcro is to take the city's founding ideals as a Christian town and harmonize them with acceptance of others and "the incorporation of different cultures and sensibilities" as the population becomes more diverse, the Pope told the townspeople huddled under umbrellas in a town square.

The Pope had arrived in Sansepolcro in the midst of a rain storm that forced him to cancel a visit to La Verna, site of a Franciscan shrine marking the place where St. Francis of Assisi received the stigmata.

Pope Benedict had started the day in Arezzo, celebrating Mass in a park with an estimated 30,000 people, including Italian Prime Minister Mario Monti.

Tuscany was the birthplace and heart of the Italian Renaissance, a humanist movement that led to a flourishing of art, music and literature. Tuscans today, the Pope said, have to ask themselves "what vision of the human person they are able to propose to new generations."

The Gospel calls Christians "to live God's love toward everyone" with solidarity, care for the weakest members of society and respect for the dignity of each person, he said.

"To be in solidarity with the poor is to recognize the plan of God the creator who has made everyone one family," the Pope said.

Pope Benedict said giving witness to God's love by caring for the weakest must include defending human life from conception to natural death and protecting the family.