Pope's first encyclical is summer bestseller
200,000 copies sold so far in Italy22 August, 16:33
The Vatican publisher, Libreria Editrice Vaticana (LEV), noted that the 200,000 figure does not even include sales of the same treatise by other authorized publishers.
While this is Francis's first encyclical, he has made it clear that much of the work in "Lumen Fidei" or "The Light of Faith" was produced by his predecessor, Benedict XVI.
"It's an encyclical written by four hands, so to speak, because Pope Benedict began writing it and he gave it to me (to complete)," Francis told bishops this summer in Rome.
Francis, the first pope from Latin America, was elected less than four months before publishing, making this encyclical something of a modern record.
It urges believers to avoid arrogance, advising that "faith is not a truth that is imposed by violence, it is not a truth that crushes the individual," but rather it "reawakens critical senses" and "broadens the horizons of reason".
The text - released just days before Francis made a much-acclaimed visit to the Italian island of Lampedusa to honour the thousands of migrants who have died fleeing North Africa - also reminded followers of the importance of Christian faith in maintaining society and its institutions.
"When faith is weakened, the foundations of humanity also risk being weakened," according to the text.
This encyclical was to have been Benedict's fourth on the theological virtues, and follows the best-selling trilogy: Deus Caritas Est (God Is Love), published in 2006, Spe Salvi (Saved in Hope), in 2007, and Caritas in Veritate (Charity in Truth), in 2009.
Citing his failing physical strength, Benedict abdicated in February, triggering the elections that brought in Francis.
For its first run, the Vatican initially intended to print 500,000 copies of the 90-page Italian edition, priced at 3.50 euros each.
The encyclical was designed as a kind of summary of the ideas from a synod that ended October 24 on the subject of the new evangelization, but also discussed "evangelization in general," according to publishers. Benedict was originally expected to complete the encyclical in the first half of 2013 but his resignation, announced to a stunned world on February 11 and carried out on February 28, made this impossible.
He is now retired and lives in the Holy See, marking the first time in history that two popes - one sitting, the other not - have lived simultaneously behind the Vatican walls.