H. P. Blavatsky
"The early Gnostics claimed that their Science, the GNOSIS, rested on a square, the angles of which represented respectively Sige (Silence), Bythos (depth), Nous (Spiritual Soul or Mind), and Aletheia (Truth).
It is they who were the first to introduce and reveal to the world that which had remained concealed for ages: namely, the Tau, in the shape of a Procrustean bed, and Christos as incarnating in Chrestos, he who became for certain purposes a willing candidate for a series of tortures, mental and physical. For them, the whole of the Universe, metaphysical and material, was contained within, and could be expressed and described by the digits of Number 10, the Pythagorean decade.
This Decade representing the Universe and its evolution out of Silence and the unknown Depths of the Spiritual Soul, or anima mundi, presented two sides or aspects to the student. It could be, and was at first, so used and applied to the Macrocosm, after which it descended to the Microcosm, or Man. There was, then, the purely intellectual and metaphysical, or the "inner Science," and the as purely materialistic or "surface science," both of which could be expounded by and contained in the Decade.
It could be studied, in short, from the Universals of Plato, and the inductive method of Aristotle. The former started from a divine comprehension, when the plurality proceeded from unity, or the digits of the decade appeared, but to be finally re-absorbed, lost in the infinite Circle. The latter depended on sensuous perception alone, when the Decade could be regarded either as the unity that multiplies, or matter which differentiates, its study being limited to the plane surface; to the Cross, or the Seven which proceeds from the ten - or the perfect number, on Earth as in heaven.
This dual system was brought, together with the Decade, by Pythagoras from India. That it was that of the Brachmans and Iranians, as they are called by the ancient Greek philosophers, is warranted to us by the whole range of Sanskrit literature, such as the Puranas and the laws of Manu. In these "Laws" or "Ordinances of Manu," it is said that Brahma first creates "the ten lords of Being," the ten Prajapati or creative Forces; which ten produce "seven" other Manus, or, rather, as some MSS. have it, Munin, instead of Manun = "devotees," or holy Beings, which are the Seven Angels of the Presence in the Western religion.
This mysterious number Seven, born from the upper triangle, the latter itself born from the apex thereof, or the Silent Depths of the unknown universal soul (Sige and Bythos), is the sevenfold Saptaparna plant, born and manifested on the surface of the soil of mystery, from the threefold root buried deep under that impenetrable soil. This idea is fully elaborated in Vol. I. § "Primordial Substance and Divine Thought," which the reader has to notice carefully, if he would grasp the metaphysical idea involved in the above symbol.
In man as in nature, it is, according to the cis-Himalayan esoteric philosophy (which is that of the original Manu Cosmogony), the septenary division that is intended by Nature herself. The seventh principle (purusha) alone is the divine SELF, strictly speaking; for, as said in Manu, "He (Brahma) having pervaded the subtile parts of those six of unmeasured brightness," created or called them forth to "Self"-consciousness or the consciousness of that One SELF. Of these six, five elements (or principles, or Tattva, as Medhatithi, the commentator thinks) "are called the atomic destructible elements"." [The Secret Doctrine by H. P. Blavatsky]