The penultimate section of Chapter IV, Rooted in God, is about devotion. Here are the concluding two paragraphs:
If we want to fix on one of the numberless examples of devotion offered to us by the saints, we can picture to ourselves St. Theresa of the Child Jesus in here last illness, dragging her fevered, wasted body night after night to the choir for the Divine Office. On the way, she would have to pass by the open cloister, swept often by a cutting wind. The Office would leave her so exhausted that it would take her over an hour to crawl—as she literally had to do—back to her straw pallet. “As long as the soldier has his feet under him,” she would say gaily, “he must be at his post.”
The way to acquire devotion is to think frequently about God as goodness and greatness and our own immediate and utter dependence on him. We can work up sensible fervor or enthusiasm by means of hymns and an organ, but we can only get our will moving by thought. A will prompt and eager to serve God and worship him will follow only from a conviction that God deserves to be served and worshipped and that it is good for us to serve and worship him. The stronger that conviction, the more ready and eager is the will likely to be. It is only daily meditation on what God is and what we are—“I am he who is, you are she who is not,” said Our Lord to St. Catherine of Siena—that will give us the conviction that begets and sustains devotions.
Anselm Moynihan, O.P., The Presence of God 38.