The number ten (10), the decad, is of profound symbolic significance, perhaps most especially to the Jewish Qabalists and the Pythagoreans, both of whom created a tenfold schema depicting the nature of the Universe and its unfolding.
Pythagoras believed that 4 contained all the secrets of the Universe, as within 1+2+3+4=10. After 10 all numbers repeat. The tetractys was the Pythagorean schema:
. .. ... ....
All things emanated from the One, the "Monad."
The Qabalists similarly employed the idea of "emanation" in their Tree of Life, which consists of "not nine, not eleven, but ten sephiroth" (Sepher Yetzirah). Sephiroth (sing. sephirah) literally means emanation.