19. The self slays not nor is slain, and thinking to the contrary is an act of bewilderment. only.                                                                                                                                                                                            Significance:                                                                                                                                                                                                                                 Being bewildered, conditioned souls have illusory assessments on all kinds of levels. And that's how they remain in the sad world of the continuously changing.

20. For the soul there’s neither birth nor death at any time. He has not come into being, does not come into being, and will not come into being. He is unborn, everlasting, primeval and original. He is not slain when the body is slain.
Significance:
Whatever takes birth is bound to die, whatever has beginning has an end, and whatever is being created is sure to be destroyed. This is how the material circumstance is arranged. In Vedanta Sutra 1.1.2 it is stated “om janmady asya yatah”: “That Supreme Brahman is He from whom the creation, sustenance and dissolution of the material universe arises”.  Anyone who understands that Supreme Brahman is liberated from entanglement, has endeavour to reach liberation from it, or is voluntarily encaged. No worries need to be there in the latter case since you'll get a new chance in the next body or perhaps after hundred bodies.

21. Oh Partha, Arjuna, how can a person who knows that the spirit soul is indestructible, eternal, unborn and immutable kill anyone or cause anyone to kill?
Significance:
Being sinless means one acts simply for the sake for acting. Ultimate responsibility is a pipe dream since we haven’t created the material universe, nor the variety within it. One simply reaps the illusory results of what one sows in the material world. Indeed, God’s infallible law of karma runs the theatre, runs the show in the material universe, no one & nothing else. Carrying out ones overall inclination in yoga, in unification with Krishna, the Absolute Truth, a person is never bewildered. And therefore beyond God’s infallible law of karma. In such a state you have no backlashes from whatever you do, your activities produce neither good nor bad results. Amnesty is indeed guaranteed in the position of actual inclusivity.

22. As a person puts on new garments, giving up old ones, the soul similarly accepts new material bodies, giving up the old ones.
Significance:
According to ones karmas one gets new temporary bodies over and over again in the material world. Certain people believe you only get one body from God. This is incorrect. Certain people die for instance at the age of 5 or 7, and up until that time have lived under comparatively sad circumstances. This while other people reach the age of 86 or 94 in relatively good health and during their lives meet all kinds of wonderful circumstances like a nice upbringing, a high quality education, a wonderful career, a nice wife and nice children, a nice bank balance, many friends etc. etc. etc.. So when God would only give everyone just one body God would be a monster, which He isn’t. And He of course explains in the Gita, among other texts, about His system of the material Universe, of which karma/reincarnation is an essential part. Then there are people who claim that the world is just a coincidence and with death everything is finished. So these people never ever need to worry about anything. And then you have people claim that evidence is based upon repetition, and so there cannot be any evidence reincarnation is a fact. These people fail to understand that repetition doesn’t exist in the observable reality.

23. The soul cannot be cut to pieces by any weapon, nor burned by fire, nor moistened by water, nor withered by the wind.
Significance:
One has to practically realise the fact that, while the body is meant for destruction, the true self is indestructible, eternal. In spiritual life it is about practical realisation. If one does not yet have practical realisation of the true, eternal self, one simply admits the fact. Honesty is of essence in practising spiritual life. It is unlimitedly better to be an honest street sweeper than to be a fake yogi, a fake religionist, or a fake philosopher.  One success, though, is instantly there when one is not honest, like you have with dry book, so called “knowledge”. That is the success of being one hundred percent successful in befooling yourself. That success is immediately there. One could of course ask oneself whether one should like to have such a success.