The laws of nature are immutable and apply to everything in nature. As an example, the first law of thermodynamics states that the total energy of any isolated system is constant. (By definition, an isolated system cannot exchange matter and energy with the surroundings)
There are laws that apply to the ātmā also. These laws apply always in all conditions that the ātmā may find itself. One such law is
The ātmā is immutable (avikāri)
It is one of the more profound laws in my opinion, because we do not find such a law in nature. I can think of no substance in nature that cannot be altered or destroyed. But the ātmā cannot be altered in any way. The law has several profound consequences listed below.
Some corollaries derived from the law of immutability of the ātmā
1. The pure ātmā cannot know anything. Because if it knows something, its state has changed from ‘not knowing’ to ‘knowing’. This change of state, a vikāra, is not allowed because the ātmā is immutable. All knowing is external to it.
2. Some argue that the pure ātmā can think. But a thought is a vikāra – a change. When we think, we are changed, in the sense that the state before the thought, and the state during the thought, is different. Such a change cannot be allowed in the ātmā. The pure ātmā cannot think by itself. All thought is external to it.
3. Likewise an experience is also a change in state – from the prior state of no experience to the state of experience. Again, this cannot be allowed. All experience is external to the ātmā. The pure ātmā cannot experience anything.
4. An action is also a change in state. Therefore the pure ātmā cannot act. All action is external to it.
5. The pure ātmā cannot love. Because love is an emotion, which involves thought. It follows that there is no love (prema) or bhakti in the pure ātmā. Bhakti and love are all external to it.
6. It follows that knowing, acting, experiencing, thinking, loving, serving, etc. all without exception occur in the mind or body which are external to the ātmā.
The law of immutability requires that the ātmā be unchanged as it migrates from one material body to another, or when it attains liberation into Brahman, or even when it gets awarded a siddha deha to serve Bhagavān. This law is very useful in recognizing apasiddhāntas of all types, keeping our concepts straight when things get confusing, and in firmly grasping how the ātmā is utterly, utterly dependent on Bhagavān for literally everything. It has no independence whatsoever.