In order to answer this question, we must first discuss symbolic interactionism. Next, we will need to define what a reference group is in sociological terms. When we have done those things, we can answer the question and say how symbolic interactionism would “explain religion as providing a reference group.”
Symbolic interactionism is one of the three major theoretical perspectives in sociology. According to symbolic interactionism, society is created by our own individual interpretations of what we experience every day. Things only have meaning because we give them that meaning.
In sociology, a reference group is a group with which we compare ourselves. It is a group that we care about and that we want to fit in with. (We can also have groups that we do not want to fit in with and we can compare ourselves to those groups as well.) We look at the behaviors of the people in our reference group and adjust our own behaviors to fit in better (or to be more completely different than the people in the group if we do not like the group).
Symbolic interactionism would say that religion would provide a reference group to us if we want it to. For example, if I believe that members of Religion A are admirable, I will decide that I want to be like them. They are a reference group simply because I say they are. Alternatively, if I hate Religion B, I will use them as a reference group and I will try to act in ways that are the opposite of how they would act. In either case, they are a reference group simply because I choose to make them one.
Symbolic interactionism would explain that religion provides us with a reference group because we say that it does. What matters is how we perceive the world. If we perceive that religion is important, we will use religion as a reference group.