"The Number is the Essence of all Things"
This sentence is attributed to Pythagoras (~ 570 - 510 a.C.). As well as the meaning of the word "cosmos" for the universe. So the number expresses the essence of the cosmos, and thus of our whole world.
The discovery of Pythagoras was: splitting a string on the monochord with the simplest integers:
1, 2, 3, 4, 5, 6, 7, 8, etc.
gives the basic notes of elementary intervals of music:
Octave, Fifth, Third, Seventh etc.
From this he gained the realization that the earthly music is
an Image of Harmony in the Cosmos .
Today we describe it like this:
By dividing the string with the 1,2,3, ... to 16 we hear the overtone row:
And form the intervals:
Octave - Quint - Third - Seventh, etc.