Francis of Assisi had a great love of the TAU. According to studies by Damien Vorreaux, the mystique of the Tau is not the product of a spontaneous germination in the mind of Francis; it is a solid acquisition of tradition. Pope Innocent III opened the Fourth Latern Council on November 11, 1215 with an admirable and eloquent sermon which immediately aroused the universal interest. As a theme he took the following words of Christ: “I have desired with a great desire to eat this Pasch with you.” (Lk. 22:15). He then recalls that the Pasch means Passover and he expresses his hope that the Council will be a Passover, a New Passover. After depicting the profanation of the Holy Places by the Saracens, Innocent deplored the scandals dishonoring Christ’s flock, threatening it with God’s punishments if it did not reform. He also gave a commentary to the Council members on Chapter 9 of Ezekiel. He made his own the words of God to his prophet: “Pass through the center of the city and mark with a Tau the foreheads of the men who weep and wail because of all the abominations which are committed there.” The Church was in a bad state during this period of history. Innocent pointed out that the Tau is the last letter of the Hebrew alphabet and its form traces a cross like the one which was presented before attaching Pilate’s placard. The Tau is the sign borne on the forehead if one is to manifest the radiance of the cross in all of one’s conduct.

Some writers believe that it was the Council that persuaded Francis that he had a role to play in the reform of the Church. Francis took the discourse of Innocent III given at the Council to be personally addressed to him. The fact is that the Tau, which the Pope made the emblem of the reform, became from then on Francis’ own blazon. He used it as a signature, painted it on his door, and placed it on his writings. The Pope said: “Mercy will be granted to those who bear the Tau, a mark of life of penance and renewal in the Church.” And so Francis wanted to sign himself with the Tau and his brothers along with him. The Tau became the sign of the Order’s mission. The Tau colored Francis’ entire spirituality, which from 1215 on, became even more a spirituality of the cross and salvation.

The Tau of penance was the favorite theme of his preaching because he considered himself as enlisted by the Pope for this crusade. Francis is very aware that the Tau is the sign of conquerors, and after having preached it, he will reproduce it even in the flesh through the Stigmata (the wounds of Christ). He will know and radiate the joy of the cross. The Tau represents for Francis the universality of salvation. The Tau is for him the symbol of permanent conversion and to total disappropriation. To be converted, to allow oneself to be marked with the Tau is to become poor. The Tau calls him to the mission and the service of others because it reminds him that the Lord himself had become our servant unto death. The Tau is for him the sign of the goodness and love of God. The Tau is for him the title of glory and the source of his perfect joy.