VATICAN CITY — Even at age 13, Pope Francis was concerned for the poor.

The Vatican newspaper L’Osservatore Romano on Wednesday published a letter Francis sent to a fellow priest in 1990 in which he recounted all the things he learned during the sixth grade year he spent studying at a Salesian school in his native Buenos Aires.

The letter is remarkable in that the then-Rev. Jorge Mario Bergoglio remembered the names of all his priestly instructors from four decades previous.

But more importantly, he remembered particular lessons, including the night in October 1949 in which he learned about death, the night he started saying his prayers before bed (and never stopped), and the depth of his adoration for the San Lorenzo soccer club.

But he also recounted having learned that year certain life lessons about piety, sexual purity and what he called the “Catholic culture” and the importance of looking out for the neediest.

“I remember having learned there to deprive myself of certain things and give them to people poorer than me,” Bergoglio wrote.

Francis has made reaching out to the poor and most marginalized the priority of his pontificate, saying the church must be like a “field hospital” for the wounded faithful, ready to welcome the neediest in with mercy.

Francis wrote the letter in 1990 while living in Cordoba, during what has been described by biographers as an exile of sorts after his difficult tenure running the Jesuit order in Argentina during the country’s military dictatorship and subsequent term as the rector of a Jesuit seminary.

The letter was written to a Salesian priest in Argentina in praise of the Salesian education Bergoglio said he received at the Wilfred Baron of the Holy Angels school in Ramos Mejia, outside the capital, amid threats that the order might turn over some of its schools to lay administrators.

The letter was recently unearthed in the archives of the Salesian order in Buenos Aires, and published in full in Wednesday’s Vatican daily.