The purpose of a committee determines its size as well as who is appointed to serve on it.
Committees are created to investigate a question, it is important that all the different views of the membership be reflected in the committee members. The practice allows many differences to be resolved in the committee instead of at the assembly meeting where they take up a lot of time.
The committee chairman is the most important member of a committee of a committee. He or she is responsible for calling the committee meetings, overseeing all the work, and completing the work.