What was Tom thinking about in the wagon when he was with Haley?

From the text:

As to Tom, he was thinking over some words of an unfashionable old book, which kept running through his head, again and again, as follows: "We have here no continuing city, but we seek one to come; wherefore God himself is not ashamed to be called our God; for he hath prepared for us a city." These words of an ancient volume, got up principally by "ignorant and unlearned men," have, through all time, kept up, somehow, a strange sort of power over the minds of poor, simple fellows, like Tom. They stir up the soul from its depths, and rouse, as with trumpet call, courage, energy, and enthusiasm, where before was only the blackness of despair.