Many of the characteristics of God have already been expressed in connection with the previous volumes 1-3 of the revelation of God and the proofs for his existence. But they were mentioned rather indirectly and systematically, and some of the facts were scarcely noted. Volume 4 examines more fully the nature of God, with special reference to his essence and attributes. For instances, the terms “essence” and “substance” are practically synonymous when used of God. They may be defined as that which underlies all outward manifestation; the reality itself, whether material or immaterial. To speak of God is to speak of an essence, a substance, not of a mere “idea” or the personification of an idea.