21 On this selfsame foundation of humility he desired that his Order of Friars Minor should be founded and built. He repeatedly taught his followers, in exhortations begotten of a truly marvelous wisdom, that they should glory in nothing, and above all not in their acquisition of virtues or in the possession of divine grace. He admonished them too, and even, on occasion, reproved those friars who because of their duties as preachers, men of letters, philosophers, superiors of convents and provinces, were exposed to the dangers of vain glory. It would take too long to go into details; this is enough to prove our point that St. Francis, following the example and words of Christ ( Matt . xx, 26, 28; Luke xxii, 26), considered humility in his followers as the distinctive mark of his Order - namely, "he insisted that his disciples be called 'Minors,' and the superiors of his Order 'Ministers.' He did this in order both to make use of the very language of the Gospels which he had promised to observe and to make his disciples understand by the name which they bore that they must go to the school of the humble Christ in order to learn humility." (St. Bonaventure, Legenda Maior , Chap. VI, No. 5)
Source: Rite Expiatis (Vatican.va)