In the begining of part two, Montag remembers clarisse. Why do the two books remind him of clarisse?

Montag and Mildred are reading on a cold November day. Montag picks up a book and reads words about friendship, "We cannot tell the precise moment friendship is formed...." Montag recalls the so authentic feelings that surfaced when he was with Clarisse. She is, however, dead and Mildred reminds him of this. His other book, "That favourite subject myself". Montag thinks of Clarisse because "her favourite subject wasn't herself". Montag recalls how Clarisse looked into him; she understood him better than he understood himself.