VATICAN CITY (AP) — Pope Francis was to mark his 50th anniversary as a priest Friday by paying homage to his spiritual father, a fellow Argentine Jesuit whose teachings on popular piety and discernment have had an enormous influence on the papacy.

Francis is scheduled to attend the book launch for a collection of writings by the late Rev. Miguel Angel Fiorito. The collection is being published by the Jesuit magazine La Civilta Cattolica, and the launch is taking place at the Jesuit headquarters near the Vatican.

In a preface to the collection, Francis wrote that “Maestro Fiorito” taught his students how to pray and discern the will of God and the signs of the time. “His school of spirituality was a school of dialogue and listening,” Francis wrote.

Francis has riled conservatives with his emphasis on the role of discernment and conscience, as opposed to black and white rules, in making tough moral decisions. Francis has also held up popular piety and a “poor church for the poor” as the true church of the “people of God.”

The former Jorge Mario Bergoglio was ordained a priest on Dec. 13, 1969 in Buenos Aires. He is history’s first Latin American, and first Jesuit pope. He is marking his 50th priestly ordination anniversary just a few days before he turns 83, on Dec. 17.