Mutual aid is the voluntary and reciprocal exchange of goods within an organization. Examples in various religious antecedents include Judaic Tzedakah, Islamic Zakat, and various Christian institutions of charity, as described in the Acts of the Apostles. Berman argues that religious organizations experience economic risks by extending mutual aid to all alleged believers—theological assent is cheap, action can be costly. By imposing a series of outwardly visible social rules, such as restrictions (or prescriptions) on dress, diet, language, and social interactions, groups impose a cost on entering into a mutual aid partnership, diminishing the occurrence of free riding.