The authors underline the importance of the print Ara poru aguĭyey haba (meaning about the good use of time) for the Jesuit missions of Paraguay and the colonial Río de la Plata. Attributed to Father José Insaurralde, it is a two-volume devotional text entirely written in Guaraní that was published in Madrid in 1759 and 1760. Until now, literature has only approached the Ara poru in a superficial and external way, because it is written in a different way from the current ones. The unpublished translation of the summary and two preliminary warnings to readers reveal that it follows the structure of Ignacio de Loyola’s Spiritual Exercises. The authors of this article demonstrate that by the mid-eighteenth century, the Jesuit project was to produce an indigenous reader and devotee in the modern sense (individual reading and personal transformation).