Humility, modesty, sobriety, purity, piety, and prudence, with meekness, ornament the soul, and make us live on earth a truly angelic life.---BL. JORDAN OF SAXONY.
Now humility makes a man a good subject to ordinance of all kinds and in all matters; while every other virtue has this effect in some special matter. Therefore after the theological virtues, after the intellectual virtues which regard the reason itself, and after justice, especially legal justice, humility stands before all others.---ST. THOMAS AQUINAS.
Explanations (by Tanquerey):
Humility considered in itself is interior to the theological virtues. It is even interior to some moral virtues.
But, if we consider humility as being the key that opens the treasures of grace and as the foundation of all virtue, it is, as the Saints say, one of the most excellent of virtues.