Ratri means “night” and Nava means “nine”. At Navaratri (“nine nights”), the Lord in the form of the Mother Goddess is worshipped in Her various forms as Durga, Lakshmi and Saraswati. Though the Goddess is one, She is represented and worshipped in three different aspects. On the first three nights of the festival, Durga is worshipped. On the following three, Lakshmi and then Saraswati Devi on the last three nights. The following tenth day is called Vijayadasami. Vijaya means “victory”, the victory over our own minds that can come only when we have worshipped these three: Durga, Lakshmi, and Saraswati.
Durga
To gain noble virtues, all evil tendencies in the mind must be destroyed. This destruction is represented by the Goddess Durga. The buffalo stands for tamoguna, the quality of laziness, darkness, ignorance and inertia. We have these qualities too. We love to sleep. Although we may have a lot of energy and potential inside us, we prefer to do nothing - just like the buffalo that likes to lie in pools of water. , The destruction of the tamoguna within us that is very difficult to destroy, we invoke that Divine Power within us to destroy our animalistic tendencies.
Lakshmi
For knowledge to dawn within us, we have to prepare our minds. The mind must be pure, concentrated, and single-pointed; this purification of the mind is obtained through the worship of Lakshmi Devi.
In our society today, however, when we think of Lakshmi, we think only of money - counting gold and dollar bills! This is why if one goes to a Lakshmi temple, one will find a crowd. Adi Shankaracharya describes six forms of wealth (calmness of mind, self-control, selfwithdrawal, forbearance, faith and single-pointed ness) that are to be cultivated to attain wisdom.
Saraswati
Victory over the mind can be gained only through knowledge, through understanding; and it is Goddess Saraswati who represents this highest knowledge of the Self. Although there are many kinds of knowledge in the Vedas - phonetics astronomy, archery, architecture, economics and so on - the real knowledge is in the spiritual knowledge. Lord Krishna himself says in the Bhagavad Gita: “The knowledge of the Self is the knowledge”;
In other words, we may have knowledge of many other subjects and sciences but if we do not know our own Self, then that is the greatest loss. Therefore the supreme knowledge is the knowledge of the Self that is represented by Goddess Saraswati.
Navaratri
Thus, at Navaratri, Goddess Durga is invoked first to remove impurities from the mind. The Goddess Lakshmi is invoked to cultivate the noble values and qualities. Finally, Saraswati is invoked for gaining the highest knowledge of the Self. This is the significance of the three sets of three nights when all these three are gained subjectively, and then there will be Vijayadasami, the day of true victory!
As we can see, the theme of the entire Vedas is reflected in the Navaratri festival: Purify the mind and remove all negativities; cultivate positive virtues; gain spiritual knowledge and transcend limitations. This is the real victory - the dance of joy - ritualistically performed at night, as it is also on Shivaratri (auspicious night), to signify our spiritual awakening.
Source: by Swami Tejomayananda