Which type of organization operates solely for the benefit of its members and their beneficiaries?

A fraternal benefit society is an organization that is established to provide benefits to its members and their beneficiaries. These societies typically operate on a not-for-profit basis and are often founded on a common bond, such as a shared religion, ethnicity, or profession. Members usually pay dues, and in return, they receive various benefits which can include insurance coverage, financial assistance, or social services. The focus of these organizations is on serving their members rather than maximizing profits, distinguishing them from other types of insurance entities.

In contrast, a mutual company also serves its members but is primarily structured as a for-profit entity, focusing on insurance products and profits while returning surplus earnings to policyholders in the form of dividends. A joint venture involves two or more parties collaborating on a specific project or business activity, and it does not primarily serve the interests of individual members or beneficiaries. A risk retention group is a liability insurance company formed by a group of businesses with similar risk exposures, which means its operation is more about sharing risks rather than focusing solely on member benefits.

The essence of the fraternal benefit society's function relates directly to its commitment to the welfare of its members, making it the correct answer to the question posed.