Private religion
"Romans... distinguished between public and private religion. When the distinction between public and private religion is applied to the Roman emperors, it becomes clear that many of them pursued personal religious interests in addition to their public religious role." [http://gradworks.umi.com/33/12/3312490.html Circa deos ac religiones: Religion and the Roman emperor from Augustus to Constantine by Polk, Matthew Robert, Ph.D., HARVARD UNIVERSITY, 2008, 412 pages; 3312490]
"It should be remembered, however, that early persecution of Christians did not follow the same prerogatives commonly ascribed to religious persecution in the modern sense, but rather arose from a feeling of "otherness" that Christians aroused in the society of the time, being adverse as they were to participating in the religious life of the Roman empire at large. Private religion, or the sacra privita, was not regulated by the state until the Christianization of the Empire, when paganism was proscribed even within the home. Private religion was the purview of the family and the individual, and varied between various ethnic groups." WikipediaA
" Private religion is on behalf of individuals, familiae and gentes as well as certain other small groups such as collegiae, guilds and sodalities."
"Private religion did not require the services of state priests, but there were several areas of overlapping between the two and they did not operate separately. Thus state pontifices would give advice on private religious matters and on inheritance passing outside a familia on the death of the last member. This was because both public and private religions were officially overseen by the state through the ius divinum. But whereas public religion was restricted to the worship of a limited number of approved gods and select festivals private religion allowed for the worship of any god and celebration of any festival providing that no breach of the peace occurred." Public and Private Religion
"Legally there was also a major difference between things dedicated to the gods as part of public and private religion; things dedicated for the people became consecrated res sacra whereas private dedications did not and so theft of such items would constitute sacrilegium in the first case but not in the second. Before examining the details of the domestic cult I must present some caveats. The picture of Roman domestic religion is clouded by the restricted nature of the evidence currently available. Thus much of our evidence comes from the Campanian towns of Pompeii and Herculaneum as well as from Ostia and Rome itself and thus a question arises as to how 'Roman' our current view of the subject actually is. " Public and Private Religion
"An established church arguably obviates a merely private religion and maintains the tradition of social responsibility."
[https://books.google.com/books?id=VrFLAwAAQBAJ&pg=PA186&lpg=PA186&dq=%22private+religion%22+constantine&source=bl&ots=zYlXqYhX1x&sig=B_pRQDdc_ki-MAK-kx7n1hdipL4&hl=en&sa=X&ved=0ahUKEwiZu83395fSAhVKlVQKHbVEDa0Q6AEINjAF#v=onepage&q=%22private%20religion%22%20constantine&f=false Disavowing Constantine : mission, church and the social order in the theologies of John Howard Yoder and Jürgen Moltmann. By Nigel G. Wright]
"This essay conceptualizes the War on Poverty as a period during which public religious capacities were incorporated into the institutional apparatus of the national welfare state. Such incorporation largely served the political needs of the welfare state itself, as it needed not only to execute but also to justify social policy to a variety of publics, including black political movements. Welfare state expansion during this period occasioned the setting of a practical boundary between public and private religion."
Rise of the Public Religious Welfare State: Black Religion and the Negotiation of Church/State Boundaries during the War on Poverty Omar M. McRoberts