"When we don't walk, we are stuck," Pope Francis said in a homily at the altar in the Sistine Chapel where the conclave of the College of Cardinals that chose him met.
Citing passages from the Psalms, the Gospel of St. Matthew and the Letter of St. Peter, he said, "When we don't build on the rock, what happens? It's what happens to children when they build a sand castle and it all falls down. When we walk without the cross, when we build without the cross and when we confess without the cross, we are not disciples of Christ. We are mundane.
"I would like for all of us, after these days of grace, that we find courage to walk in the presence of God ... and to build the church with the blood of Christ. Only this way will the church move forward."
Francis began his first full day as pope with a visit to the Santa Maria Maggiore Basilica in Rome.
The Rev. Ludovico Melo, a priest who prayed with him, said the pontiff spent about a half-hour at the basilica, a special place for Jesuits, which included singing a hymn and spoke to people in the church to go to confession, the Italian news agency ANSA reported.
"Mercy, mercy, mercy," the Argentine pope said, Melo indicated.
Pope Francis, the first South American pope elected Wednesday after five votes at the conclave, also prayed before a famous icon of the Virgin Mary called the Salus Populi Romani, ANSA said.
New York Archbishop Timothy Dolan, who participated in the conclave, said Pope Francis was to travel to the papal summer residence at Castel Gandolfo outside Rome Thursday to meet his predecessor, Pope Emeritus Benedict XVI, who resigned at the end of February, citing health and age.
The schedule indicates Francis, 76, was to meet with cardinals – both who participated in the conclave and those who did not -- on Friday. ANSA said he will lead his first Angelus, a Catholic devotional, as pope in St. Peter's Square on Sunday. His inaugural mass is scheduled for Tuesday.
Francis, the former Cardinal Jorge Mario Bergoglio who was the archbishop of Buenos Aires, told the cardinals following the conclave Wednesday that one of his first acts as pope would be a visit to his predecessor.
U.S. Vice President Joe Biden and his wife, Jill, plan to be at the inaugural mass and lead the U.S. delegation, the White House said.
Biden said in a statement the Catholic church played "an essential role in my life," not just in matters of faith but also "in pursuit of peace and human dignity for all faiths."