2:29 "One sees him in a vision of wonder, and another gives us words of his wonder. There is one who hears of his wonder; but he hears and knows him not.
There are some who can readily envision and understand the concept of the soul, and some who are able to speak at length about the nature of the soul. Yet there are those who have heard all about the soul and do not believe in it.
Having a soul does not automatically make one aware of its existence, nor its properties.
2:30 "The Spirit that is in all beings is immortal in them all; for the death of what cannot die, cease thou to sorrow."
The soul exists in all beings, not just people, and it is immortal in all beings. While the existence of a soul in people is not in dispute in other religions, the presence of a soul in an animal is not widely accepted (at least by religious leaders. Pet owners have their own ideas).
2:31 "Think thou also of thy duty and do not waver. There is no greater good for a warrior than to fight in a righteous war."
Having explained about the soul, Krishna moves on to speak of duty. We know already that Arjuna is a warrior. That is his path. Unlike Christianity, which argues that a man's fate is a foregone conclusion, predestined or predetermined, Hinduism holds that a man has a place in life, a dharma, yet he makes choices to adhere to his duties or stray from them all his life. Thus, while it may be that life is revered, a warrior fighting a righteous war is free from stain on his karma for killing because he was merely fulfilling his duty. If that same warrior were to kill a romantic rival in cold blood, the death would certainly not be righteous.
It also brings up the concept that a war may be righteous.
2:32 "There is a war that opens the doors of heaven, Arjuna! Happy the warriors whose fate it is to fight such a war.
2:33 But to forgo this fight for righteousness is to forgo thy duty and honor: is to fall into transgression."
Not only is a warrior free from stain on his karma for fulfilling his duty in fighting a righteous war, but if he demurs, his soul does not advance in this life.
-Death is not to be mourned, for the soul is immortal
-killing another person is okay, even required, in the context of being a warrior doing one's duty
-war is okay if for a righteous purpose.