The present essay must be regarded as a sequel to the "Destiny of Man,"--so much so that the force of the argument in the concluding section can hardly be appreciated without reference to the other book. The two books, taken together, contain the bare outlines of a theory of religion which I earnestly hope at some future time to state elaborately in a work on the true nature of Christianity. Some such scheme had begun vaguely to dawn upon my mind when I was fourteen years old, and thought in the language of the rigid Calvinistic orthodoxy then prevalent in New England. After many and extensive changes of opinion, the idea assumed definite shape in the autumn of 1869, when I conceived the plan of a book to be entitled "Jesus of Nazareth and the Founding of Christianity,"--a work intended to deal on the one hand with the natural genesis of the complex aggregate of beliefs and aspirations known as Christianity, and on the other hand with the metamorphoses which are being wrought in this aggregate by modern knowledge and modern theories of the universe. Such a book, involving a treatment both historical and philosophical, requires long and varied preparation; and I have always regarded my other books, published from time to time, as simply wayside studies preliminary to the undertaking of this complicated and difficult task. While thus habitually shaping my work with reference to this cherished idea, I have written some things which are in a special sense related to it. The rude outlines of a very small portion of the historical treatment are contained in the essays on "The Jesus of History," and "The Christ of Dogma," published in the volume entitled "The Unseen World, and Other Essays." The outlines of the philosophical treatment are partially set forth in the "Destiny of Man" and in the present work. It amused me to see that almost every review of the "Destiny of Man" took pains to state that it was my Concord address "rewritten and expanded." Such trifles help one to understand the helter-skelter way in which more important things get said and believed. The "Destiny of Man" was printed exactly as it was delivered at Concord, without the addition, or subtraction, or alteration of a single word. The case is the same with the present work. PETERSHAM, _September 6, 1885_. CONTENTS. _I. Difficulty of expressing the Idea of God so that it can be readily understood_ _35_ _II. The Rapid Growth of Modern Knowledge_ _46_ _III. Sources of the Theistic Idea_ _62_ _IV. Development of Monotheism_ _72_ _V. The Idea of God as immanent in the World_ _81_ _VI. The Idea of God as remote from the World_ _87_ _VII. Conflict between the Two Ideas, commonly misunderstood as a Conflict between Religion and Science_ _97_ _VIII. Anthropomorphic Conceptions of God_ _111_