When Montag was a child, a cousin challenged him to fill a sieve, which is a kitchen utensil used to drain items and has a lot of holes in it, with sand. As he filled the sieve, the sand drained out. He was promised a dime if he could fill the sieve.
"And the faster he poured, the faster it sieved through with a hot whispering." (pg 78)
The memory came back to him as he is sitting on a train heading for Faber's house. He has suddenly come to the realization that books are important and that men spent a lot of time writing down ideas and those ideas needed to be saved. He makes an analogy with the sand and sieve to his efforts to memorize the Bible.
"If you read fast and read all, maybe some of the sand will stay in the sieve. But he read and the words fell through..." (pg 78)
He realized that in a few hours he would have to turn the book over to Beatty, and he only had a few hours to memorize as much as he could. He willed himself to memorize as much as he could. At the end of the book, when he meets Granger, he says,
"I thought I had part of the Book of Ecclesiastes and maybe a little of Revelation, but I haven't even that now." (pg 150)
Granger assures him that when it is needed, he will remember. He does remember after the bomb hits. He becomes the Book of Ecclesiastes.