The materialistic form of absolute energy is strength. Woman is true strength. Any creation evolves from the embryo of eternal energy. This energy provides the universe its inspiration and capacity. When Shiv (male energy) associated with Shakti (female energy) it balances the universe. However, an imbalance between the two, leads to degeneration.
In order to ignite the existing energy within, one needs to remove the soot that must have gathered on it. Abstinence during the navratra has been suggested for cleaning of one’s mind and inner-self. Abstinence also means fasting and praying to God.
Since we are going through environmental transition, the body experiences an increase in bile. Fasting for nine days helps clean the inner body, removal of all faults/abnormalities. The body receives the desired nourishment through fruits and righteous diet. Meditation, reverence help clean up while devotion improves the essence of mind. Sacrifice and offerings to the fire god helps eliminate the unwanted organisms in the environment. Walking barefoot gives us the energy (element) held by the earth.
Autumnal navratra is a festival also associated with agriculture. The farmer obtains a hint from the nature helping him select the right kind of crop for the seson. This is done by sowing nine different cereals in nine different sets of soil (ghat).
There is a useful meaning hidden behind every festival celebrated in Indian culture. And hence, the navratras herald the festivities that help store energy for the rest of the year.