From one of his most popular works:
Therefore he who wishes to ascend to God must, avoiding sin, which deforms nature, exercise the above-mentioned natural powers for regenerating grace, and do this through prayer. He must strive toward purifying justice, and this in intercourse; toward the illumination of knowledge, and this in meditation; toward the perfection of wisdom, and this in contemplation. Now just as no one comes to wisdom save through grace, justice, and knowledge, so none comes to contemplation save through penetrating meditation, holy conversation, and devout prayer. Just as grace is the foundation of the will's rectitude and of the enlightenment of clear and penetrating reason, so, first, we must pray; secondly, we must live holily; thirdly, we must strive toward the reflection of truth and, by our striving, mount step by step until we come to the high mountain where we shall see the God of gods in Sion [Ps., 83, 8].