When Church writers no longer felt bound to exert all their powers of argument against Rome or rival modes of Protestantism, and when disputes about forms of government, rites, and ceremonies, and other externals of religion ceased to excite any strong interest, attention began to be turned in good earnest to the deeper and more fundamental issues involved in the Reformation.  There arose a great variety of inquiries as to the principles and grounds of faith.  Into all of these entered more or less directly the important question, How far man has been endowed with a faculty of spiritual discernment independent of what is properly called reason.  It was a subject which could not be deferred, although at this time encompassed by special difficulties and beset by prejudices.  The doctrine of ‘the inner light’ has been in all ages the favourite stronghold of enthusiasts and mystics of every kind, and this was more than enough to discredit it.  All the tendencies of the age were against allowing more than could be helped in favour of a tenet which had been employed in support of the wildest extravagances, and had held the place of highest honour among the opinions of the early Quakers, the Anabaptists, the Muggletonians, the Fifth Monarchy men, and other fanatics of recent memory.  Did not the very meaning of the word ‘enthusiasm,’ as well as its history, point plainly out that it is grounded on the belief in such inward illumination?  And who, with the examples of the preceding age before him, could foretell to what dangerous extremes enthusiasm might lead its excited followers?  Whenever, therefore, any writers of the eighteenth century had occasion to speak of man’s spiritual faculties, one anxiety was constantly present to their minds.  Enthusiasm seemed to be regarded with continual uneasiness, as a sort of unseen enemy, whom an incautious expression might let in unawares, unless they watchfully guarded and circumscribed the province which it had claimed as so especially its own.

It is certainly remarkable that a subject which excited so much apprehension should have entered, nevertheless, into almost every theological discussion.  Yet it could not be otherwise.  Controversy upon the grounds of faith and all secondary arguments and inferences connected with it gather necessarily round four leading principles—­Reason, Scripture, Church Authority, Spiritual Illumination.  Throughout the century, the relation more particularly of the last of these principles to the other three, became the real, though often unconfessed centre alike of speculation and of practical theology.  What is this mystic power which had been so extravagantly asserted—­in comparison with which Scripture, Reason, and Authority had been almost set aside as only lesser lights?  Is there indeed such a thing as a Divine illumination, an inner light, a heavenly inspiration, a directing principle within the soul?  If so—­and that there is in man a spiritual presence of some