Montag sees a campfire used for warmth.

Montag fantasizes about Faber, a man who has not bought into society’s ideas about happiness.  Most of the population lives in the city, and there is “open country” near the river “in the fields and hills” and open countryside (Part 2).  When he floats in the river, he feels at peace because he is in nature, and he is surrounded by the natural instead of the unnatural.

When Montag leaves the river, he sees a different kind of fire.  This fire is used by the people for warmth.  The people are not afraid of it.  They hold their hands up to it.  They are obviously controlling it.  Montag is amazed.  He never thought of fire as anything but destructive.

He hadn't known fire could look this way. He had never thought in his life that it could give as well as take.  (Part III)

Montag describes the fire as strange because it “it meant a different thing to him.”  All of his life he has looked at the world one way.  He has been taught to fear the unknown, and respect and fear fire.  He has been told that if something is different, it’s destructive.  People can’t be happy if they have to think for themselves, or if they are different.

Montag makes a rash move in killing Beatty and running away to join the book people, but Mildred forces his hand when she turns him in.  Everything he knew about life has been questioned since he met Clarisse, so it is no wonder he thinks about her during his time by the river when he sees the strange fire.  Montag clearly has what it takes to adapt, and become something most people in his society are not capable of imagining.

The juxtaposition of Montag’s amazement at seeing fire used in ways readers consider ordinary and the ordinary way Montag uses fire that readers consider unusual reminds the reader of the parallels between this world and our own.  Although their society has made different choices than ours, we are in fact not so different after all.

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.