But when the race was farther advanced, so as to be able to act more by reason and on _general principles_, and when His religion, by new motives and forces, was to be extended from one nation to all the world, _then the Creator came himself_; and while disclosing those most terrific sanctions of the invisible world, at the same time exhibited such a manifestation of His pity, sympathy, and _self-sacrificing love_ as renders these terrors safe and effective in such a conjuncture, as they would not be without. With these two classes of motives thus intensified, such a moral power has been generated, leading to self-denying efforts to educate and save mankind, as never existed before. In the case of the writer, the power of these terrible sanctions _alone_ has been illustrated. In other cases, the power of Christ's love and example have been the leading motives. It is the _union of both_, clearly appreciated, and especially brought to bear on those who form the character of childhood and youth, that eventually is to renew the whole race, and bring every human being to perfect obedience to _all_ the laws of the Creator. * * * * * In the investigation which originated at the time the writer commenced teaching mental philosophy in connection with the Bible, this was the first point to which attention was led, "What is that '_reason_' or '_common sense_' which is so often appealed to as the umpire in religion, morals, and interpretation?" All the works of mental science within reach were examined, but it was long before any clear conceptions on this question were gained, and still longer before any _test_ was evolved that seemed a _practical_ one, as it is presented in this work. Not that these principles and the test are not indicated by metaphysicians in various forms of language, but that there is such a confusing variety of expression, and all is so presented as a _speculative_ instead of a _practical_ question, that years elapsed before that use of these principles which this work illustrates was attained. This is here referred to in explanation of future passages that otherwise might seem to imply that the author assumes to have discovered something not before known or recognized by metaphysicians. The very writings of Dr. Reid, which, in early life, were turned over with wonder that any one could be interested in them, probably contain the most complete and clear exhibition of these principles, and also recognize the _test_ by which they are to be established. The writings of Sir William Hamilton exhibit other, but less practical tests of these principles.