This threefoldness in the reader’s mind corresponds to the threefoldness of the work (Book-as-Thought, Book-as-Written, Book-as-Read), and that again to the original threefoldness in the mind of the writer (Idea, Energy, Power). It is bound to be so, because that is the structure of the creative mind. When, therefore, we consider Trinitarian doctrine about the universal Creator, this is what we are driving at. We are arguing on the analogy of something perfectly familiar to our experience. The implication is that we find three-fold structure in ourselves (who are the Book-as-Read), because that is the actual structure of the universe (which is the Book-as-Written), and that it is in the universe because it is in God’s Idea about the universe (the Book-as-Thought). Further, that this structure is in God’s Idea because it is the structure of God’s mind.
There is nothing mythological about Christian Trinitarian doctrine: it is analogical.Dorothy Sayers, The Mind of the Maker, pp. 122 – 123