It is a work done by Kingsley Davis and Wilbert Moore (1945). It is one of the most popular works in Structural Functionalism.
Davis and Moore said that social stratification (e.g. class structure) is universal and necessary.
Functional question: How does a society place people in their proper positions in the stratification system?
Their finding: In order to be sure people occupy the higher-rank position, society must provide various reward such as prestige, high salary, sufficient leisure.