Pope Francis is reminding priests to always be merciful, as he ordained 16 men in a ceremony in St. Peter's Basilica.

In remarks Sunday to the new priests from several nations, Francis said: "Please, don't tire of being merciful" since they themselves sin.

Pope Francis blesses new priests during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. (AP Photo/Alessandra Tarantino)

Pope Francis blesses new priests during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. (AP Photo/Alessandra Tarantino)

He told them to work only in service to God for the good of the faithful.

Encouragement toward mercy and selfless service is a hallmark of Francis' 5-year-old papacy.

Pope Francis blesses new priests during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. (AP Photo/Alessandra Tarantino)

Pope Francis blesses new priests during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. (AP Photo/Alessandra Tarantino)

Francis gripped a hand of each man as, one by one, they knelt before him. He asked if they promised "me, and my successors, filial respect and obedience." They each replied, "Yes, I promise."

Priests pray during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. Pope Francis is reminding priests to always be merciful, as he ordained 16 men in a ceremony in St. Peter's Basilica. In remarks Sunday to the new priests from several nations, Francis said: "Please, don't tire of being merciful" since they themselves sin. (AP Photo/Alessandra Tarantino)

Priests pray during a ceremony in St. Peter's Basilica at the Vatican, Sunday, April 22, 2018. Pope Francis is reminding priests to always be merciful, as he ordained 16 men in a ceremony in St. Peter's Basilica. In remarks Sunday to the new priests from several nations, Francis said: "Please, don't tire of being merciful" since they themselves sin. (AP Photo/Alessandra Tarantino)

Pedophile priests and church hierarchy's cover-up of sex abuse have stained the Catholic church's reputation and tested Francis' own ability to combat the problem.