Pope Francis has exhorted the faithful to avoid being smug or "lukewarm" Christians.

Francis celebrated Mass in St. Peter's Basilica on Saturday to mark the feast day of the Apostles Peter and Paul, Rome's patron saints. The pope encouraged humility among the faithful.

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Pope Francis holds his pastoral staff as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis has exhorted the faithful to avoid being smug or "lukewarm" Christians.

Pope Francis meets prelates as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

He told faithful to avoid becoming "lukewarm Christians living by half measures."

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Prelates follow a Mass celebrated by Pope Francis in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Prelates follow a Mass celebrated by Pope Francis in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

A Swiss Guard stands attention as Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

A Swiss Guard stands attention as Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds up the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds up the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass with blessing of the palliums, in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass with blessing of the palliums, in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Francis said "whenever we consider ourselves smarter or better than others. That is the beginning of the end."

Pope Francis holds his pastoral staff as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds his pastoral staff as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

He told faithful to avoid becoming "lukewarm Christians living by half measures."

In a June 29 tradition, Francis blessed white, wool stoles destined for churchmen who were named as metropolitan archbishops in the past year.

He also that the presence of a delegation of Orthodox prelates at the ceremony "reminds us that we can spare no effort also in the journey toward full unity among believers."

Pope Francis meets prelates as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis meets prelates as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Prelates follow a Mass celebrated by Pope Francis in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Prelates follow a Mass celebrated by Pope Francis in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

A Swiss Guard stands attention as Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

A Swiss Guard stands attention as Pope Francis celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds up the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds up the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass with blessing of the palliums, in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis celebrates Mass with blessing of the palliums, in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)

Pope Francis holds the book of Gospels as he celebrates Mass in St. Peter's Basilica at the Vatican, Saturday, June 29, 2019. (AP PhotoGregorio Borgia)