The ruling ideas of each age have ever been the ideas of its ruling class.
When people speak of the ideas that revolutionise society, they do but express that fact that within the old society the elements of a new one have been created, and that the dissolution of the old ideas keeps even pace with the dissolution of the old conditions of existence.
When the ancient world was in its last throes, the ancient religions were overcome by Christianity. When Christian ideas succumbed in the 18th century to rationalist ideas, feudal society fought its death battle with the then revolutionary bourgeoisie. The ideas of religious liberty and freedom of conscience merely gave expression to the sway of free competition within the domain of knowledge.