There are two main reasons why the stratification in socio-economic status is also reflected in stratification in church affiliation. First, there tend to be differences in the way that upper class people feel and think when compared to lower class people. Second, there is a strong tendency in the United States for people to want to mingle with others who are “like them” in important ways. Both of these factors help to create a situation in which church affiliation is linked to socioeconomic status.
In the US, richer people tend to belong to the older, more “mainline” churches. These are churches that typically put a higher degree of emphasis on education and on rational thinking with regard to religious issues. These are churches that tend to be less fundamentalist and less focused on issues of traditional morality such as homosexuality or abortion. This sort of church is more likely to appeal to a person who is highly educated and who tends to want to seek a religion that makes logical sense. By contrast, poorer people are more likely to accept religious ideas that may not seem rational but which can be accepted on faith. Since the people from different classes tend to have somewhat different worldviews, they tend to be more comfortable in different churches.
In general, America is becoming more segregated along class lines. We are less likely than we once were to live near to or come in close contact with people from socioeconomic circumstances that are very different from our own. We are less comfortable interacting with people who are very different from us. This change in our attitudes helps to bring about segregation in religious affiliation. We tend to gravitate towards churches that are filled with people who are “like us.”
For these reasons, the stratification in our socioeconomic status tends to be reflected in our church affiliation.