All popes tend to have a couple of catchphrases they invoke time after time, so after a while they come to sum up a whole chunk of his thought. "Be not afraid!" was such a phrase for John Paul II, and "reason and faith" for Benedict XVI.
It's becoming steadily clearer that for Francis, perhaps his core signature phrase is the "culture of encounter."
The pope invoked the term again Friday in a brief year-end audience with Italian diplomatic staff and the Italian embassy to the Holy See.
"Allow me to underline a prospective that I consider very important," Francis told the diplomats.
"You're in a position to promote the culture of encounter," he said. "You're diplomatic personnel and all of your work is designed to allow representatives of countries, international organizations and institutions to encounter one another in the most effective way."
"How important is this service!" the pope said.
Francis asked the Italian diplomats to bring Italy's cultural patrimony in art and civilization to bear in spreading a culture of encounter.
Like many sound bites, the "culture of encounter" is elastic enough to embrace a wide range of possible meanings, but in general Francis seems to intend the idea of reaching out, fostering dialogue and friendship even outside the usual circles, and making a special point of encountering people who are neglected and ignored by the wider world.
"Encounter" is thus, in some ways, a proxy for "mercy" – placing the emphasis on compassion rather than, in the first instance, judgment.
Francis has used the language of a "culture of encounter" in too many venues to count.
He used it in a homily during his morning Mass at the Casa Santa Marta in May, for instance, in a passage that made headlines around the world because the pope said that the Lord redeemed everyone, including atheists.
The phrase "culture of encounter" figured prominently in the pope's rhetoric during his July trip to Brazil, where he often contrasted it with what he called a "throw-away culture," meaning a society in which whole categories of people – the elderly, the ill, the poor, and so on – are regarded as disposable.
In September, Francis chose "encounter" for the Vatican's World Communications Day in 2014, which most Catholic venues around the world will mark on June 1.
The "culture of encounter" is such a defining idea for Francis that saying somebody's part of it is almost the highest praise he can bestow.
In May, for instance, the leaders of the Focolare movement joined Francis for his morning Mass, and afterwards one of them spoke to the pope, telling him that the prayers of all the focolarini are with him and that they're committed to going out and building bridges with others.
"That's just what we need," Francis replied, "the culture of encounter!"
People who pay close attention to papal vicissitudes have clued in that the "culture of encounter" is a cornerstone to his worldview. Cardinal Francis George, for instance, made the point in a recent interview with the Chicago Tribune.
"He wants bishops to be part of this culture of encounter — encountering Christ and therefore encountering those that Christ loves," George said.
"Once you have the relationship, then the ideas make sense. Otherwise, it's a debating society. So you don't start with the idea. You start with a person and relationship. The pope is reminding us of this."
Cardinal Joseph Zen of China recently said that Francis projects the idea of a "culture of encounter" in his own personality, especially his seemingly endless zest for passing time with ordinary people.
"He is so true, he's so direct, straightforward, sincere, and he really wants to be in contact with people, to meet people," Zen said. "He calls it 'the culture of encounter'."
If you're looking for three words that sum up a great deal of what Francis sees himself to be about, therefore, you could do much worse than "culture of encounter."
(Follow John Allen on Twitter: @JohnLAllenJr)