This is an important scene in the story because this is where Montag meets Clarisse. Clarisse is the person who gets Montag thinking about books and changed his point of view on society. She made him curious about everything and if he didn't meet her Montag wouldn't have helped society.
This is another important scene because this is realized he messed up by reading the book out loud to Mildred's friends. This has a big part because if he didn't show the women the book it wouldn't have gotten to captain Beatty and he wouldn't have gone to Montags house.
Lastly this is an important scene because this is when Montag is running away from the mechanical hound to survive. He luckly escapes him by swimming in the lake to get rid of his scent.