George and Lennie are migrant farm workers and through them Steinbeck dramatises the plight of a large number of people who headed to California in search of work in the nineteen-thirties, when this story is set. The grim economic depression of these times, coupled with dire farming conditions in many of the Great Plains states drove whole families off their land. However things did not really improve for them much in California, and they were generally looked down upon. Steinbeck covered such cases in his work as a journalist.
The abiding sense of impermanency of the migrant workers' lives, as they drifted around from place to place chasing work - which was generally seasonal - is brought out vividly in the characters of George and Lennie. The modest aim of such people, simply to get a bit of land and settle down, takes on all the quality of a utterly splendid and enticing vision with these two characters. They have a bit of hope because unlike other migrant workers who are completely alone, they have each other (a point that George always emphasises to Lennie) but still it's not enough to make the dream come true. Steinbeck gives us two memorable characters in Geoge and Lennie but his larger purpose is to illustrate the hardships of a whole section of American society in the nineteen-thirties - something which he would do on an epic scale in his next novel, The Grapes of Wrath.