Nor has the activity of reason used in defence been less manifest in these later movements. The great works on the Christian evidences are the witness to its presence; and the deeper and truer appreciation of Christianity now shown in every country, and the increasing interest felt in religion, are the indirect effect, under the guidance of divine Providence, of the stirring of the religious apprehension by controversy.(73) We have thus at once exhibited the province which will be hereafter investigated in detail, and stated the general law observable in the conflict between free thought and Christianity. The type reappears, perpetuated by the fixity of mind, though the form varies under the force of circumstances. Christianity being stationary and authoritative, thought progressive and independent, the causes which stimulate the restlessness of the latter interrupt the harmony which ordinarily exists between belief and knowledge, and produce crises during which religion is re-examined. Disorganization is the temporary result; theological advance the subsequent. Whatever is evil is eliminated in the conflict; whatever is good is retained. Under the overruling of a beneficent Providence, antagonism is made the law of human progress. The restriction of our inquiry to the consideration of the free action of reason will cause our attention to be almost entirely confined to the operation of reason in its attack on Christianity, to the neglect of the evidences which the other office of it has presented in defence; and will also exclude altogether the study of struggles, where the opposition to Christianity has rested on an appeal to the authority of rival sacred books; such for example as the conflict with rival religions like the Jewish (4) or Mahometan (5); as well as of heresies which, like the Socinian (6), claim, however unjustly, to rest on the authority of the Christian revelation. The law thus sketched of this struggle needs fuller explanation. We must employ a more exact analysis to gain a conception of the causes which have operated at different periods to make free thought develop into unbelief. It will be obvious that the causes must depend, either upon the nature of the Christian religion, which is the subject, or of the mind of man, which is the agent of attack. The former were touched upon in the opening remarks of this lecture, and may be reconsidered hereafter;(74) but it is necessary to gain a general view of the latter before treating them in their application in future lectures.