Mahākālī is Adya Shakti in the pantheon of Dasa Mahavidya-s. She is the Mother from which all else has come, the first point of creation, an eternity of existence, and the undisputed mastery of the occult worlds.
Sri Aurobindo writes beautifully on the spiritual significance of Mahākālī, while describing the four most powerful aspects of the Divine Mother.
Mahākālī is of another nature.
Terrible is her face to the Asura, dangerous and ruthless her mood against the haters of the Divine; for she is the Warrior of the Worlds who never shrinks from the battle. Intolerant of imperfection, she deals roughly with all in man that is unwilling and she is severe to all that is obstinately ignorant and obscure; her wrath is immediate and dire against treachery and falsehood and malignity, ill-will is smitten at once by her scourage.
Indifference, negligence and sloth in the divine work she cannot bear and she smites awake at once with sharp pain, if need be, the untimely slumberer and the loiterer. The impulses that are swift and straight and frank, the movements that are unreserved and absolute, the aspiration that mounts in flame are the motion of Mahākālī.
Her spirit is tameless, her vision and will are high and far-reaching like the flight of an eagle, her feet are rapid on the upward way and her hands are outstretched to strike and to succour.
For she too is the Mother and her love is as intense as her wrath and she has a deep and passionate kindness. When she is allowed to intervene in her strength , then in one moment are broken like things without consistence the obstacles that immobilise or the enemies that assail the seeker.
If her anger is dreadful to the hostile and the vehemence of her pressure painful to the weak and timid, she is loved and worshipped by the great, the strong and the noble; for they feel that her blows beat what is rebellious in their material into strength and perfect truth, hammer straight what is wry and perverse and expel what is impure or defective.
But for her what is done in a day might have taken centuries; without her Ananda might be wide and grave or soft and sweet and beautiful but would lose the flaming joy of its most absolute intensities. To knowledge she gives a conquering might, brings to beauty and harmony a high and mounting movement and imparts to the slow and difficult labour after perfection an impetus that multiplies the power and shortens the long way.
Nothing can satisfy her that falls short of the supreme ecstasies, the highest heights, the noblest aims, the largest vistas. Therefore with her is the victorious force of the Divine and it is by grace of her fire and passion and speed that great achievements can be done now than hereafter.