A form of mother, Kalaratri is extremely frightening to look at but she is always auspicious in effect. This is why she is otherwise known as Subhankari (doing good). So the devotees need not feel any fear from her.
On the seventh day of Navaratra the worship of Kalaratri form is prescribed by the scriptures. This day the mind of the striver reaches Sahasrara Cakra. For such a striver the door of all Siddhis of the universe start opening. This day the Sadhaka with all his faculties is identified with the mother Kalaratri. As a result of her direct vision the devotee becomes quite fit to earn all sorts of virtues. All his sins and obstacles in his way are completely destroyed. He attains the abodes which are the fruit of inexhaustible virtues.
The mother, Kalaratri destroys the wicked. Danava, Daitya, Raksasa, Bhuta, Preta and all other evil spirits are terrified and run away as soon as the devotee remembers Kalaratri. She is also the remover of planetary evil effects. Her worshipper has no fear from fire, water, wild beings, enemy or night. By her grace he always remains unmindful of any fear.
By keeping her form in the heart and meditating on her the devotee must worship her single-mindedly. He should observe all Yamas, Niyamas and Samyamas (all rules and regulations). Purification of mind, words and body is essential in her worship. She is Subhankari. The auspicious effects emanating from her worship are innumerable.