Kali at her essence is the only goddess in the Hindu Pantheon not dominated by a male presence. She is, first and foremost, defined by her individual, female will. Her strength is shown in terms of how she is known by her devotees: simultaneously nurturing & destroying. At the same time it was necessary to show her in human terms, to make the images accessible and almost mundane. The first reaction is intended to be a human one--how her carriage and her gestures are recognizable & what they say of an indomitable (and potentially cruel) power.
Siva, among many other aspects, is a consort to Kali. In a famous story from the Kali canon, it is Siva who stops her from destroying the world. When Kali saves the world by destroying a demon, she enters a bloodlust state in which she starts destroying everything, good & bad. Siva, simply by lying down, naked in the battlefield, breaks Kali from her path of annihilation. His beautiful, prostate form is the antidote to her self-possessing destruction. The same aforementioned humanness of image exists here in a Godot-like state of waiting, in an action of inaction. The self-captive male energy acts as foil to the feminine will.
Sati was Siva's first wife and his first love. Sati fell in love with and married Siva. Siva, a goat herder at the time, was refused by Sati's father as a suitable spouse for his daughter. He did not acknowledge their union. Later on, the father organized a grand feast for family and friends and invited neither Sati nor Siva. This infuriated Sati who attended regardless. Father and daughter engaged in an argument on the suitability of her husband Siva. Seeing no resolution, Sati immolated herself before her father and his guests. She robbed her father of a daughter and attained a morbid victory over him. A lesser-known aspect of this story is that the Sati who goes to the feast is a ghost projection of Kali (Sati is sometimes depicted as a manifestation of Kali). By killing herself, she only kills an illusion, thus punishing the father but maintaining the integrity of her being. This is the flip side of the power of the will. Instead of pushing outward, this pulls inward--a solipsistic strength that, although self-harming, is equally incontestable. Here, the environment folds in on the individual: the body is defined by its reaction rather than its projection and motives are occluded.