Though ever dwelling in the unseen kingdom, he was keenly alive to the tendency of the intellectual world around him. His saintliness, and his great ability, seem to have pointed him out as destined to sway the philosophical and theological tendencies of an age in which the human mind was in a condition of flux. The corroding rationalism of the school of Abelard, and the dissolving mysticism of the East, had to be faced, and to be withstood. Thomas fixed himself, therefore, on the immoveable basis of authority, and grounded his teaching on the monastic methods of the "Sentences." Doubtless the surprise caused by his distinctions, and the admiration created by his novelty in argument, proceeded in great measure from his vivid apprehension of the work he had to do, of the enemy he was contending with, and of the powers by which alone that enemy could be overthrown. He followed Albert, but his teaching was more incisive, more definite, more strictly to the point. Many of his disciples became distinguished men. S. Thomas assisted others beside his own pupils. Sovereigns, cardinals, bishops, superiors of orders, and professors, wrote to him for advice, and for solutions of their difficulties. The Opusculum on the difference between the Divine and human word; and the somewhat larger treatise, on the nature of the intellectual word, are full of close reasoning; and state principles which are fundamental regarding the method of human knowledge. One of the most important of his treatises is that addressed "ad Fratrem Rainaldum," on the nature of the Angels. It was begun during his bachelorship, but he never got beyond the 30th chapter. It shows his grasp of some of the cardinal questions of the day, and how masterfully he dealt with errors of the most promising minds in the Paris schools. But whilst thus engaged upon the Scriptures and the Lombard, S. Thomas was frequently in the pulpit, and he regularly delivered lectures to crowded halls. His versatility, his power of abstraction, his astonishing memory, his zealous husbanding of time, carried him with ease through works which would have broken the spirit of any ordinary man. He possessed that marvellous gift which Origen and Cæsar are said to have had, of being able to dictate to three or even four scribes on different and difficult subjects at the same time, and that, too, without losing the thread of each argument. Frigerius says that, as Professor, he elucidated the Sentences with such sublimity of thought that he seemed rather the author of the work than its expositor. Tocco, "that he surpassed all the masters of the University, and by the lucidity of his expositions drew, beyond all others, the intelligences of his disciples towards a love of science." Students from every part of Europe flocked around his chair.