The nine-day fight is a symbolic story of man’s quest for Perfection (Siddhi) as the divine element battles through the layers of ignorance and the forces of Darkness and Night. These are the nine stages of the soul’s inner journey as is evident from the names itself.
Shailbala is the daughter of the mountains signifying the birth of the Divine Energy within matter. She is hidden in matter lying concealed at the base of the spine in man. When she awakens, then man begins to turn towards higher spiritual things. His quest begins with the awakening of this fire as the Vedic seers would say.
The next stage is Brahmacharini whence we have to tend and safeguard this newborn aspiration by becoming more and more one-pointed.
As a result the night of ignorance in which we dwell becomes lit up. This is the Chandraghanta.
The fire has to be further held within and further concentrated like a baby in the womb. This is Kushmanda, the cosmic egg.
The next step is the delivery of the psychic being or the secret soul in us. The Divine Power working in us delivers the soul out of the prison of the ego and is called Skandamata.
It is after this that man or a woman becomes a power of Durga, Katyayani to fight the cosmic battle against the demons and forces of Mahishasura.
Once the battle against the cosmic forces of darkness are accomplished, then the next step is surrender at the feet of the Divine Mother who takes away from us the entire burden of good and evil as Kalaratri.
It is then that we perceive her in Her true original form as MahaGauri, the effluent Mother giving birth to the gods in us.
Finally, all these powers are taken up to their utmost possible individual perfection by the Grace of the Divine Mother as Siddhidhatri.
The final victory indeed takes long but the beauty of the story is that in the end Mahishasura realises his end is near. He then throws himself at the feet of the Divine Mother in complete surrender. The mood of the Divine Mother now changes into Compassion and she not only slays the outer form of Mahishasura but takes his inner being into hers and assures that he will be kept near her in all her worship. This image reveals that the highest aspect of Durga is indeed the power of Compassion rather than the power to slay. Her destruction is also a Grace and even her punishment is a blessing.
About Savitri | B1C3-07 Workings of the New Consciousness (p.28)