What Montag had been able to memorize was part of the Bible. In specific, he had been able to memorize the Book of Ecclesiastes from the Old Testament. Actually, he had not really memorized it and was worried that he would be of no use to the rest of the "book covers." But they reassured him. They told him that they had ways of helping him remember and that he would be very important to them.
Montag also said that he thought he had parts of the Book of Revelation from the New Testament. For whatever reason, they do not include that in what they think he knows.
I'll answer the first part of your question and let another editor answer the second.
In Fahrenheit 451, after escaping the city and the mechanical hound brought in to hunt him, Montag follows railroad tracks after getting out of the river. The fire he sees is a campfire, and he notes that it is different from fire as he had experienced it, it was a "different thing."
This fire was warming, not destroying. He sees hands near the fire, being warmed. He never realized that fire could give back, not just take. He notes that even the smell of the fire is different from what he was use to.