Bhagawān Krishna gives Arjuna another way of looking at the situation. Even if one assumes that the Self is repeatedly born and dies, death is still an inevitable part of the cycle. Therefore, excessive grief is not appropriate.

जातस्य ध्रुवः मृत्युः — for one who is born, death is certain.
ध्रुवं जन्म मृतस्य च — for one who has died, birth is certain.

Krishna points out the natural cycle of birth and death.

ध्रुवः means certain, fixed or inevitable. Krishna emphasizes that death is certain for one who is born.

अपरिहार्ये means unavoidable / inevitable. Krishna says that when something is unavoidable, excessive sorrow over it is not useful.

Krishna is not saying that we should become emotionless. He is teaching us to recognize what is within our control and what is not. Grieving over something unavoidable cannot change the outcome.

Krishna describes three stages:

Before birth → अव्यक्त (unmanifest)
During life → व्यक्त (manifest)
After death → अव्यक्त (unmanifest)

Therefore, why should one excessively grieve over this natural process?

अव्यक्त means unmanifest / not available for perception. Before birth, the being is not available to us in a manifest form.

Chāruvākas are sweet talking nāstikās who do not believe in ātma or rebirth.

As per the Dharma śāstram, death is only a Vikāram, change from one state to another.

According to Kṣaṇikavijñānis Consciousness is flickering / momentary