Petri told CNA that Pope Francis is speaking in continuity with recent popes including Pope St. John Paul II, who issued "a very strong statement" about capital punishment in his 1995 encyclical Evangelium Vitae; he said that the death penalty should only be used "when it would not be possible otherwise to defend society," but added that because of improved security in prisons, "such cases are very rare, if not practically non-existent."
Popes John Paul II and Francis have worked with the "prudential application" of the Church's magisterial teaching on the authority of the state, Fr. Petri said, and not reversed it.
The Church has historically taught that the "primary reason for punishment" is "retribution," he said, which is not revenge but "the idea that the punishment has to fit the gravity of the crime." Secondary reasons for punishment included the rehabilitation of the criminal and the protection of society.
John Paul II put "protecting society" at the "front and center" of the Church's teaching on punishment, Petri said, and Pope Francis has continued this teaching in his magisterium, which reflects a new understanding of punishment.
Many in society view the death penalty now "simply about protecting society from killers and people who are dangerous, being a deterrent, and maybe rehabilitation," Petri said, and supporters of the death penalty's continued use should consider if "it cultivates or curries in them emotions of revenge," which "is not retribution."
While Popes Francis and John Paul II are making prudential applications of the Church's teaching in areas of faith and morals, the level of assent required to their teaching is not just "prudential," Petri explained.
When a cleric takes a profession of faith before becoming a pastor or a dean of a seminary, he said, he must assent to not only divine revelation and definitive propositions of Church teaching on faith and morals, he said, but also the teaching of the pope and bishops exercising the authentic magisterium.
"That's more than just giving it the benefit of the doubt, it's basically saying 'I'm going to subscribe my intellect and will to what you're teaching even if I don't understand it, I'm going to try to understand it.'"
For a teaching that has been repeated frequently in statements and high-level documents, including in the Catechism, it's hard to dismiss assent as merely a matter of prudence, Petri said.
"You can probably disagree with whether or not there should be life prison terms, but not this. I don't think you can say this about the death penalty issue."