The biography of the St. Francis tells us how this singular prodigy of the Stigmata came about. Around the Feast of the Exaltation of the Holy Cross, just two years prior to his death, the Seraphic father went up on this mountain, in order to begin his Lenten fast which he was accustomed to do in honor of St. Michael, the Archangel.
Wishing ardently to know the will of the Lord and be wholly configured to Christ, he opened thrice the book of the Gospel in the name of the Holy Trinity. Because each time he opened it to the section on the Passion of the Lord Jesus, he prayed incessantly to feel on his body the pain of the Crucified. He, then, had a vision, which filled him with great joy and, at the same time, with a deep sorrow.
It was a vision of the Lord in the form of a Crucified Seraph who revealed that he (Francis), too, would be wholly transformed into the image of Christ Crucified. Once the vision was over, there appeared on the flesh of this friend of Christ the signs of the Passion of the Lord, namely, the nails which pierced through his hands and feet, and the wound on his side (cf. LMaj XIII, 1ss). .