If the life-force is not destroyed by death, what happens to it?
“When the soul relinquishes its old form, it takes on a new form, just like you get new clothes to replace old ones that have worn out.  Life-force can never be destroyed or damaged: you can’t cut it with a blade; you can’t burn it with flame; nor can you dissolve it in water; nor erode it with the wind.  The unbreakable, unburnable, insoluble, un-erodible life-force pervades everything and is everlasting, immovable and eternally unaffected.  The self-realized describe it as non-manifest, beyond-conception, and without transformation. So, if you understand this, why should you lament? ”
The key here is “if you understand this.” The soul is beyond direct perception and conception. Only the self-realized can deeply understand and explain it. So what if I don’t have deep faith in their explanation, or my ability to understand their explanation? What if I am not convinced that life-force is absolutely indestructible? Krishna will address this now.
“Even if you think life is constantly being created and destroyed; even still, O hero, why would you fall into lament?  If living beings come to life from nothingness, then when they return to nothingness after death, what is there to regret? ”
If life is destroyed at death it becomes nothing. If there is thus no continuous soul, it means that living things emerge from nothingness. This means that life, when destroyed, returns to the state from which it began. In turn, this means that life would again arise. Just as it was once created from nothing, once it returns to the same situation surely it will again be created. So, in this Krishna explains a different angle on reincarnation which does not require belief in an eternal soul.
Now that Krishna has presented two versions of reincarnation – one involving an eternally distinct soul, and another not involving such a thing – Arjuna would want to know which theory Krishna prefers. So he says:
“There are many, many opinions about the soul, because the soul is amazing and very difficult to understand, either by direct perception, inference, or discussion.  But my friend, take it from me: eternal and indestructible life-force dwells within all bodies. Therefore you need not truly grieve for any living being. ”
Some twist statements like these to suggest that Krishna is undermining the principles of compassion. That is very unreasonable and lacks any broad understanding of the cultural context surrounding Krishna and Arjuna. In that context humility, compassion and service to others is the very foundation of human ideals. What Krishna is saying here is that there is nothing truly disastrous or grievous that befalls any living being – for the true living entity is highly insulated from the illusory body he or she identifies with; even though that body is subject to almost constant threat of disasters. It is, actually, the identification of the soul with the body that deserves the lamentation and compassion of a wise person.