We come at last to Christianity. What is its principle or essence? This question must be answered or we cannot judge of it aright.
Now, during the eighteen centuries of its history, Christianity has taken so many and such various forms, it has received so many developments in every sense, it has become a thing so rich and luxuriant, that it is far from easy to discover beneath this thick growth of institutions, dogmas, ceremonies, and devotions the tap-root of the tree from which it all has sprung, and from which it still derives its nutriment. It would be next to useless to interrogate the Churches. They would each answer according to their official theologies and Confessions of Faith. This, they would say, is the essence of Christianity. The Catholics would say it is the institution and infallible authority of the Church, because everything rests on this first foundation, and because no one can be in Christian truth who is outside the Church. The Protestants would not be agreed: one would propose the dogma of Justification by Faith; another the authority of Scripture; a third the metaphysical divinity and the eternal pre-existence of Jesus Christ, under the pretext that they could not conceive the possibility of the subsistence of Christianity without these dogmas. In entering on this examination we enter on an interminable dispute.
The problem, happily, is simplified for the historian and the psychologist. In asking what is the principle of Christianity, what do we wish to know? Simply what it is that makes a Christian a Christian. We desire to ascertain what is the inward element, present in the soul, which compensates, at need, for the absence or defect of all the rest, and which, being wanting, cannot be supplied or compensated for by anything else. In short, we want to get at the religious experience which determines and marks out the consciousness of all Christians, which makes them members of one moral family, and which makes them to be recognised as such in spite of differences of times and place, of language and of culture, of rites and even of beliefs. To seize this common feature there is no need of polemics; all we need is a little history and psychology.