"The Christian student is as conscious of direct intercourse with Jesus Christ as with the external world, or with other minds. This is the very postulate of living Christianity. It is a datum or revelation made to a spiritual faculty in the soul, as real as the external senses or any of the mental or moral faculties, and far more exalted. This living contact with a living person by faith and prayer is, like all other life, ultimate and mysterious, and must be accepted by him in whom it exists as its own sufficient explanation and reason, just as the principles of natural intelligence and conscience, to which it is something superadded, and with which, in this point of view, though in other respects higher, it is co-ordinate. No one who is living in communion with Jesus Christ, and exercising that series of affections towards Him which Christianity at once prescribes and creates, can doubt the reality of that supernatural system to which he has been thus introduced; and nothing more is necessary than to appeal to his own experience and belief, which is here as valid and irresistible as in regard to the existence of God, of moral distinctions, or of the material world. He has no reason to trust the one class of beliefs which he has not, to trust the other.... To minds thus favoured, this forms a _point d'appui_ which can never be overturned--an _aliquid inconcussum_ corresponding to the '_cogito ergo sum_' of Descartes. Their faith bears its own signature, and they have only to look within to discover its authenticity. Philosophy must be guided by experience, and must rank the characters inscribed on the soul by grace at least as sacred as those inscribed by nature. Such persons need not that any man should teach them, for they have an unction from the Holy One; and to them applies the highest of all congratulations: 'Blessed art thou; for flesh and blood hath not revealed it unto thee, but My Father which is in heaven.'"[12] [Footnote 12: _Fragments of College and Pastoral Life_, pp. 38-40.] These words contain the true explanation of Cairns's life. There was in it the "_aliquid inconcussum_"--the "unshaken somewhat"--which made him independent of other arguments, and which kept him untouched by all the intellectual attacks on Christianity. Other people who had not this inward testimony, or who, having it, could not regard it as unshaken by the assaults of infidelity, he could argue with and seek to meet them on their own intellectual ground; but for himself, any victories gained here were superfluous, any defects left him unmoved. Was it always so with him? Or was there ever a time when he was carried off his feet and had to struggle for dear life for his Christian faith amid the dark waters of doubt?