The number nine is the enneagon; it is the Ninth Sphere. It is related with Mars in the Ninth Sphere. Here one begins a fight within oneself against everything, against nature, because here in the Ninth Sphere, demons and gods are made. One must descend into the depth of the infernos in order to build the solar bodies.

The ninth constellation, Sagittarius, corresponds to the number nine. Its metal is iron, its stone is the carbuncle, its color is red, its musical note is Re in the second octave.
The coronary plexus corresponds to the number nine, as well as the creative organs, the gonads.
The work in the Ninth Sphere has an objective: to create the solar bodies. One has to comprehend that even when an individual has built the bodies, immortality has not been achieved as a result.
In order to gain immortality, to have worked in the dissolution of the ego is needed, because otherwise one is converted into a Hasnamuss with a double center of gravity. These are abortions of the Cosmic Mother who enter into the infernal worlds till reaching the Second Death.
It is necessary to achieve the elimination of the ego and the three traitors. One realizes what the ego and the three traitors are when one reaches 100% consciousness.
The red demons of Seth must be reduced to cosmic dust. It is necessary to verify absolute death, because if some subjective element remains alive, then the deceased is called to order.
Those who have died in themselves are received in the world of the dead.
To the number nine belongs emotion, wisdom, generosity, geniality.
Finally, we have zero, which is eternity, the Universal Spirit of life.

One has to operate with all of the numbers in Kabbalah.
The number is holy, infinite and eternal.
He that hath an ear, let him hear what the Spirit saith unto the churches; to him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God. - Revelation 2: 7