The monistic theory of the universe—the theory that One is All, and that All is One;
that one Substance manifests itself as the seeming many elements of the material world—
is of Hindu origin, and has been gradually winning its way into the thought of the Western world for two hundred years.
It is the foundation of all the Oriental philosophies, and of those of Descartes, Spinoza, Leibnitz, Schopenhauer, Hegel, and Emerson.
The reader who would dig to the philosophical foundations of this is advised to read Hegel and Emerson for himself.
The Science Of Getting Rich: 1910 by Wallace D. Wattles, Introduction, Paragraph 3

The monistic theory of the universe