ROME (CNS) -- Rome is unique and has a vocation as a universal city, Pope Francis said.

Rome has "a universal spirit" that aims to be at the service of charity, hospitality and welcome, he told the city's mayor and government officials in Rome's City Hall.

"Pilgrims, tourists, migrants, those in serious difficulty, the poorest, the lonely, the sick, the imprisoned and the excluded are the most authentic witnesses of this spirit," which is why the pope will be opening a holy door in a prison for the Holy Year 2025, he said in his speech in the city's Julius Caesar Hall June 10.

Authority is only fully realized "when it serves everyone, when it uses its legitimate power to meet the needs of the citizens, particularly the weakest and the least," he said. This applies not only to political figures, but also to priests and bishops, who must be "close to the people of God in order to serve them, to accompany them."

Making his second official visit to Rome's City Hall five years after his first, Pope Francis was accompanied by Rome Mayor Roberto Gualtieri from his vehicle to look out over the Roman Forum from an archway at the city government's headquarters.

Ancient Roman culture undoubtedly exhibited a number of "good values," the pope told city officials. But it was also seeking something more and "Mount Olympus was no longer enough," referring to where the Greeks and Romans believed their pagan gods lived.

"A larger and deeper message of fraternity, love, hope and liberation" was found in Christ and his Gospel, he said. And the Christian faith "would in time permeate and transform the lives of people and institutions themselves."

Institutions and customs evolved "to a higher level, abandoning little by little, for example, … slavery," which even educated and empathetic people had seen as natural and as a given.

Slavery is a very significant example of how "even refined civilizations can present cultural elements that are so ingrained in the mentality of people and society as a whole that they are no longer perceived as contrary to the dignity of the human being," the pope said.

This also happens today, he said, "when, almost unconsciously, we sometimes risk being selective and partial in the defense of human dignity, marginalizing or discarding certain categories of people, who end up finding themselves without adequate protection."

The pope expressed his hope that "Rome continue to manifest its true nature, a welcoming, hospitable, generous and noble face."

"The enormous influx of pilgrims, tourists and migrants into the city, with all that it entails in terms of organization, could be seen as a burden, an obstacle that hinders the normal flow of things. In reality, all of this is Rome, its uniqueness in the world, its honor, its great attraction and its responsibility toward Italy, the church and the human family," he said.

"The immense treasure of culture and history lying in the hills of Rome is the honor and obligation of its citizenry and leaders, and it expects to be properly valued and respected," he said.

As the city prepares to host the Holy Year 2025, it will attract even more people of faith for "a prayerful and penitential pilgrimage" and tourists "who come to admire its immense treasure of works of art and the grandiose traces of past centuries," he said.

In fact, "the upcoming Jubilee can also have a positive impact on the very face of the city, improving its decorum and making public services more efficient, not only in the center but fostering a connection between the center and the outskirts," he said.

"That is why I like to go and visit the outlying parishes, so that they feel that their bishop is close to them," he said.

The pope also signed the guest book quoting from the Aeneid by the Roman poet, Virgil, with "et sublato patre montem petivi" (carrying my father, I took to the hills). The verse, which the pope refers to often, describes Troy's hero, Aeneas, leaving his sacked city with his father and son -- representing his past and future -- to eventually settle in Italy, south of Rome.

With this decision to leave Troy, the pope wrote, referring to the Roman legend, "Rome was born, born from afar, born on a journey."