But difficulty for the spiritual life and thought may come, also, from ignoring the difference of the religious problem from the philosophical problem, as ordinarily conceived. I am confident, that many serious difficulties arise from the silent assumption, even on the part of theistic and Christian thinkers, that philosophy as commonly conceived is an inference from all accessible data; but this assumption is plainly erroneous. We forget that philosophy, as commonly taught, even in our avowedly Christian colleges, intentionally ignores and abstracts from all those facts that are involved in what we call historical revelation.
Now, it cannot be doubted that it is a perfectly legitimate and valuable question to ask, What may I learn about the ultimate source of things, about the meaning of the world and men, wholly apart from the facts of the so-called historical revelation? But we may never forget that the question so put is a partial one, and deliberately sets aside the most important and vital facts of the world—the preeminent spiritual facts of the race, the world's greatest teachers, as a matter of fact, in religion. It simply puts outside of its data such very significant and indubitable facts—on any possible theory—as Amos, Hosea, Isaiah, and Jesus. Now a philosophy, I submit, that ignores these facts, is plainly not all-embracing in its survey of data, and, therefore, in the nature of the case, cannot expect a complete solution, and cannot be an adequate final philosophy for life or thought.
If, however, we choose to restrict the term philosophy, as is commonly done, to the partial inquiry which ignores the most stupendous facts of the race—and I do not quarrel with the usage, provided we clearly understand it—then philosophy must look to theology for its own completion, as the only systematic inquiry that means in very truth to build upon all the data. I know nothing that, on either scientific or philosophical grounds, can justify us in expecting a satisfactory conclusion from an inquiry into the meaning of the world, that totally ignores the supremely significant fact of the world—the man Jesus, to say nothing of the line of prophets that preceded him. Whatever one's point of view, as data for a discernment of the meaning of things, these great personalities, it would seem, ought to count quite as much as things and events. And Paulsen is not without some perception of this fact; for, after speaking of various dogmas and opinions often asserted to be of the essence of Christianity, he can say, "But if I am allowed to say what I mean and to believe what I can understand and conceive, then, unmindful of the ridicule of the scoffer and the hatred of the guardian of literalism, I may, even in our days, confess to a belief in God who has revealed himself in Jesus. The life and death of Jesus make plain to me the meaning of life, the meaning of all things in general; but that which enables me to live and shows me the import of life I call God and the manifestation of God. The most upright, truthful, and liberal-minded man may subscribe to all that, to-day, as openly as ever before."
Let the thinker and seeker in religion, then, simply take account of the common restriction of philosophy, as it has already taken account of science's self-restriction. These restrictions do not hold for the spiritual life, and do not and cannot bind it in its conclusions. The spiritual can and must regard all data and ask the final questions.
It may not be in vain, in concluding the discussion upon the difference of the religious problem and knowledge from the scientific and philosophical, to summarize briefly the relations of science and philosophy to theology, as I conceive them.
Both philosophy and theology raise ultimate questions,—that is, are not confined to phenomena. Both deal with ideal interpretation, rather than mechanical explanation. Philosophy is the science of sciences, as using all sciences (properly including that of religion) as its data; but it raises questions outside the range of science proper.
So theology uses especially data from the science of religion, and in this sense is a science; but it raises questions beyond that or any other science.
A really adequate philosophy would have to take account of all facts, including those of the history of all religions, preeminently the greatest, and must culminate in the question of God. So conceived, philosophy would include theology.
But, as commonly conceived, philosophy excludes all the facts of revelation, and therefore to complete itself, must look to theology. Theology, then, becomes the crown and culmination of both science and philosophy—itself both a science and philosophy of religion and of God, who is the ultimate explanation of all.
The difference of the religious problem from the aesthetic and ethical can be best seen in the later study of the natural conditions of the spiritual life.
In the consideration of the removable causes of the seeming unreality of the spiritual life, we turn now to the discussion of the unreality which is due to mistaking the nature of the spiritual life itself.
 Paulsen: Introduction to Philosophy, pp. 250-251.