As letters to the editor go, it was certainly out of the ordinary, stretching to more than 2,500 words and not one of them veering on the irate or indignant. But the missive received by Eugenio Scalfari, co-founder and former editor of the Italian newspaper La Repubblica, nonetheless made it into print on Wednesday – on the front page and under the impressively brief byline of "Francesco".

Responding to a series of questions asked in the summer by Scalfari, who describes himself as an interested "non-believer", Pope Francis used his trademark conciliatory tone to discuss the Catholic church's attitude to atheists, urging those who do not share his faith to "abide by their own conscience" and reminding them God's mercy "has no limits".

Expressing the belief that it was important for Christians to engage in "a sincere and rigorous dialogue" with atheists, Francis recalled Scalfari had asked him whether God forgave those "who do not believe and do not seek to believe".

"Given – and this is the fundamental thing – that God's mercy has no limits, if He is approached with a sincere and repentant heart," the pope wrote, "the question for those who do not believe in God is to abide by their own conscience. There is sin, also for those who have no faith, in going against one's conscience. Listening to it and abiding by it means making up one's mind about what is good and evil."

Now in his sixth month as pontiff, Francis has made a conciliatory style and pragmatic openness to dialogue with groups on the margins of the church's traditional activities one of his trademarks.

In May, however, relaxed remarks during a homily, which appeared to imply that non-believers could be "saved" if they did good, prompted a swift clarification from the Vatican that he meant nothing of the kind.

The pope had had "no intention of provoking a theological debate on the nature of salvation", it said, adding: "They cannot be saved who, knowing the church as founded by Christ and necessary for salvation, would refuse to enter her or remain in her."

The generally moderate tone of the Francis era – and his willingness to discuss some of the touchy subjects of the church – appear to be shared by the man who will next month start work as his secretary of state, a position often likened to the Vatican's prime minister.

Pietro Parolin, an Italian archbishop, has raised eyebrows by acknowledging that "modifications" to the law of priestly celibacy might be possible under Francis's reform agenda. In comments to the Venezuelan newspaper El Universal, Parolin – who is the outgoing nuncio, or papal ambassador, to the Latin American country – said that as celibacy was a "church tradition" as opposed to dogma, it could be legitimately discussed.

"We can talk, reflect, and deepen on these subjects that are not definite, and we can think of some modifications, but always with consideration of [church] unity, and all according to the will of God," he was quoted as saying.

Francis, meanwhile, is keeping up communications with the outside world. The 76-year-old is reported to begin phone calls to ordinary people who have written to him with the words: "Hi, it's Pope Francis here."

Aside from a heavy postal bag, the former Cardinal Jorge Bergoglio occasionally receives rather larger gifts. An Italian priest, Father Renzo Zocca, has given the pontiff his old Renault 4 which, all in white, is suitably papal and has 190,000 miles (300,000km) on the clock. Francis took a spin in it around the Vatican on Saturday.

"The security staff next to me were very concerned because they understood that from now on he'll be going around the Vatican in my car," Zocca told the Catholic magazine Famiglia Cristiana. "Anyway, I also left him some snow chains in the boot. You never know."