Just as without the monad there is in general no composition of anything, so also without it there is no knowledge of anything whatsoever, since it i… - Iamblichus

Hence the Pythagoreans in their theology called it sometimes "universe," sometimes "heaven," sometimes "all," sometimes "Fate" and "eternity," "power" and "trust" and "Necessity," "Atlas" and "unwearying," and simply "God" and "Phanes" and "sun."
They called it "universe," because all things are arranged by it both in general and in particular, and because it is the most perfect boundary of number, in the sense that "decad" is, as it were, "receptacle," just as heaven is the receptacle of all things, they called it "heaven" and, among the Muses, "Ourania."

Furthermore, the monad produces itself and is produced from itself, since it is self-sufficient and has no power set over it and is everlasting; and it is evidently the cause of permanence, just as God is thought to be in the case of actual physical things, and to be the preserver and maintainer of natures.

The Triad has a special beauty and fairness beyond all numbers, primarily because it is the very first to make actual the potentiality of the Monad — oddness, perfection, proportionality, unification, limit.