First of all, the soul is eternal; cannot be killed or destroyed. Secondly, you must always do your duty. It's the lifestyle, if you are a warrior you have to kill or if you are a teacher you have to teach. Finally, after knowing the themes, style and other literary analysis we can finally answer the question of why the verses were written. Arjuna's situation is an analogy for us. Lord Krishna is trying to tell us that we can be in Arjuna's position (have to kill someone) or across the road (be killed). But we need not worry in any situation. Since this is not the end, our Atman will continue to live forever, but what we will achieve after that will depend on our karma, if we have lived according to God, then we will have achieved good karma and will have a good next life and a step towards the liberation from samsara but if we have not lived in reverence of God due to our dualistic world, for this reason Lord Krishna teaches us the different ways to achieve moksha in the rest of the Bhagavad