The following paper is dedicated to the topic of biblical motifs in Francesco Petrarca’s letters, which belong to an ubi leones sphere in historical literary research both in Poland and the whole of Europe. If we are to believe the modest and critical confessions made by Petrarca in his writings, the author of Canzoniere was rather slow in realising the importance of an in‑depth study of the Bible, and he regarded the awareness of this ignorance as gross negligence (damnosa tarditas), which made him blind for the inestimable value of the holy books. References to various biblical passus and pericopes in Familiares and Seniles are rarely used by Petrarca as purely elocutive ornaments or testimonies of his erudition, more frequently playing the role in the area of inventionis of an epistolary structure. From among all the biblical books, Petrarca most frequently and most willingly reached in his letters for The Book of Psalms, which he used (like Saint Augustine) in a very specific argumentation as an authoritative testimony of sapiential character. Biblical characters and motifs, as well as ‘winged words’, derived from prophetic books, the Gospels and Saint Paul’s letters are often found in Petrarca’s letters, which are deeply imbued with thoughts on ultimate matters, painful struggles with one’s own weaknesses, and a dramatical relationship between man and God.