The word 'religion' is not defined in the Constitution. We must go elsewhere, therefore, to ascertain its meaning, and nowhere more appropriately, we think, than to the history of the times in the midst of which the provision was adopted. The precise point of the inquiry is, what is the religious freedom which has been guaranteed.
...
In the preamble of this act (
Virginia Statute for Religious Freedom (1786) by Thomas Jefferson, 12 Hening's Stat. 84) religious freedom is defined; and after a recital 'that to suffer the civil magistrate to intrude his powers into the field of opinion, and to restrain the profession or propagation of principles on supposition of their ill tendency, is a dangerous fallacy which at once destroys all religious liberty,' it is declared 'that it is time enough for the rightful purposes of civil government for its officers to interfere when principles break out into overt acts against peace and good order.' In these two sentences is found the true distinction between what properly belongs to the church and what to the State.