Basically, we have an increasing number of people today who are not active Christians who nevertheless celebrate holidays like Easter, Christmas, etc... who are aware of the faith due to family background, personal experiences, and the social and cultural environment in which they grew up but are generally not practitioners anymore.
Is it possible that we could have that trend earlier and much larger in history in any way, where Christian identification is more of a cultural aspect than an actual community of believers? Perhaps with the likes of the Deists, or undercutting events like the American Awakenings?