Born on 14 September 1596 in Belmonte, in the region of Toledo in Spain, Juan del Castillo began studies for the legal profession at the University of Alcalá, but discovered, at the beginning of his career, a very different goal.

At Ijuí, presently in the western Brazilian municipality of Rio Grande do Sul, Juan helped Christianize the Guaranis, and taught the youngest to read and write.

[11] Juan del Castillo along with Roque Gonzalez de Santa Cruz and Alfonso Rodriguez were beatified by Pope Pius XI in 1934.

The following is an excerpt from the homily of John Paul II during the canonization Mass in Asuncion (Paraguay): Tireless in preaching, austere in their personal lives, the love of Christ and the indigenous people led them to open new roads and raise reductions that facilitated the spread of the faith and ensured dignified living conditions for their brothers and sisters.

...The work of the Jesuit fathers enabled the Guarani peoples to pass, in a few years, from a state of semi-nomadic life to a singular civilization.