It’s a deep concept in Tantra.
The image of Goddess Kali with Shiva & Mahakal shows a very deep concept in Tantra. These 3 aren't 3 but actually 1 Ultimate Truth represented in 3 forms.
Firstly, Shiva is depicted lying down in Shavasana, above him is Mahakal who is Shiva himself but in a more intense and fierce form. Above Mahakal, it's Maa Kali who is seated.
It is actually the depiction of the energies.
Firstly, Shiva as the auspicious, benevolent one serves as the base. This is the calm, peaceful force, the Consciousness.
Above him is Mahakal, the fierce form of Shiva who is the controller of time, he is the Ultimate Ruler who brings the transformation, the necessary change and evolution. Above Mahakal is Mahakali, his Queen, the Ultimate Energy who acts as the unstoppable force who makes things happen.
Now this depiction is not about superiority of one over the other, it is the perfect depiction of the static, still Aadhara (Shiva) upon which the active forces Mahakal (Shiva) and Kali (Shakti) function.
The idea is that when you are absolutely still (Shiva), it serves as the foundation for the transformation (Mahakal) and then you turn into the unstoppable, uncontrollable force (Kali). So the peaceful, calm and stable Shiva serves as the base for the transformation (Mahakal) who then eventually becomes Mahakali. Kali (Shakti) is Shiva himself at 100% femininity (dynamic force) when Shiva puts down his masculinity to 0 level (static), the more stable and still remains, his Shakti emerges from him with more intensity.
Mahakal is the perfect balance, equilibrium between the inactive state of Shiva and the unstoppable force of Kali. The union of Shiva and Shakti is the perfect representation of the functioning of Prakriti over Purush as the Aadhara (Base).
This depiction serves as a great lesson in understanding the basic Tantra in a sense that if you want to be unstoppable in growth, if you want nothing to control you then you must have a solid base which leads you to a transformation into that powerful personality. It can be understood in this way too.
So Shiva and his Mahakal swaroop along with Kali are the forces within us that make us function properly. Without Shakti, there is no life, we would be Shava (corpse) and without Shiva, there is no stability, we’ll be wild and crazy. For functioning, Energy is needed but to hold that energy, consciousness is needed. That's the play of consciousness and energy that together make things happen properly.
Jai Mahakal 🙏 Jai Mahakali 🙏