Meaningful quotes in novels cannot be defined in a universal way. Each reader will come to identify different passages (quotes) as meaningful for different reasons. When defining quotes as meaningful, a reader must justify the importance of the quote based upon why the quote is meaningful. That said, one can universally identify quotes which are meaningful based upon specific characteristics (or themes) defined within a text.
In regards to John Steinbeck's novel Of Mice and Men, many quotes can be found within chapters one and two which speak to the themes relevant to the text.
The two following quotes are important given they physically describe the main characters of the novel.
The first man was small and quick, dark of face, with restless eyes and sharp, strong features...Behind him walked his opposite, a huge man, shapeless of face, with large, pale eyes, and wide, sloping shoulders; and he walked heavily, dragging his feet a little, the way a bear drags his paws.
Here, readers are able to construct mental images of the characters of George and Lennie. Therefore, these quotes are important given they physically identify the characters for the reader.
As readers come to "know" the characters better, they become aware that Lennie is not quite right. His attraction to small and furry animals is important. While seemingly simplistic, the relationship between the weak and the strong is important in the novel.
Toward the end of chapter one, George tells Lennie about their dream (also letting the reader in on their plans). The opening of the story is sad--given it details the solitude men like George and Lennie feel.
“Guys like us, that work on ranches, are the loneliest guys in the world. They got no fambly. They don’t belong no place."
This quote sets up one of the themes depicted throughout the novel: loneliness.
Most of chapter two contains dialogue between the ranch hands. In this dialogue, readers come to find out about all of the ranchers. Candy is an aging rancher with an equally aging dog. Curley is the boss's son, full of arrogance and ego. Slim is the most respected worker on the ranch. Crooks is a black man who was injured working (and readily reminded about his secondary status). Curley's wife is a woman who the ranchers stay away from (given their fear of Curley). All of this information is given in quotes throughout the chapter. Therefore, each quote defining the characters is meaningful given it describes the characters for the reader.