Two years before his death, St. Francis retired to mount Alverno where he began a fast of 40 days in honour of St. Michael the archangel. And lo! in the midst of his meditation he saw a figure like a seraphim with six wings dazzling and burning, whose feet and hands were nailed to a cross. Aware that suffering is incompatible with the immortality of a seraphic spirit, he understood this to mean that he would become more like Jesus and bear his cross after Him (Gospel), not by physical martyrdom, but by a mystical kindling of divine love.
And in order that this crucified love might become an example to us all, five wounds resembling those of Jesus on the cross appeared on his feet, hands and side. From the latter blood flowed abundantly. The facts were so fully authenticated later, that Benedict XI ordered them to be commemorated every year, and Paul V to kindle in the faithful the love of Jesus crucified, extended the feast to the whole Church.
Mihi autem absit gloriari, nisi in cruce Domini nostri Jesu Christi: per quem mihi mundus crucifixus est, et ego mundo. * Voce mea ad Dóminum clamávi: voce mea ad Dóminum deprecátus sum.
But God forbid that I should glory, save in the Cross of our Lord Jesus Christ: by whom the world is crucified to me, and I to the world. I cried to the Lord with my voice: with my voice I made supplication to the Lord. (Galatians 6:14, and Psalm 141:2)
Domine Jesu Christe, qui frigescente mundo, ad inflammandum corda nostra tui amoris igne, in carne beatissimi Francisci passionis tuae sacra stigmata renovasti: concede propitius: ut ejus meritis et precibus crucem jugiter feramus, et dignos fructus paenitentiae faciamus.
O Lord Jesus Christ, who when the world was growing cold, in order that our hearts might burn anew with the fire of Thy love, didst in the flesh of the most blessed Francis renew the sacred marks of Thy passion; mercifully grant, that by his merits and prayers, we may ever carry our cross, and bring forth fruits worthy of penance. (Collect from Mass)
Deus, qui mira crucis mysteria in beato Francisco Confessore tuo multiformiter demonstrasti: da nobis, quaesumus, devotionis suae semper exempla sectari, et assidua ejusdem crucis meditatione muniri.
O God, who in divers ways, didst show in blessed Francis, Thy confessor, the wonderful mysteries of Thy cross, grant, we beseech Thee, that we may ever follow the example of his devotion, and be strengthened by constant meditation on that same cross. (Postcommunion)
The Catholic Encyclopaedia on the Mystical Stigmata: http://www.newadvent.org/cathen/14294b.htm
Saint Francis Of Assisi Embracing The Crucified Christ - Bartolome Esteban Murillo -
The Museum of Fine Arts of Seville, Spain