In plain words
“Well then, will you say: when the bodies that have lived together in companionship all these days are seen no more, will grief not come? If you set about grieving like that, for how many will you grieve? Pleasure and pain are like night and day. You must bear them with steadiness; for if you say ‘go away’, they will not go, and if you say ‘come’, they will not come. This pleasure and pain belong to those who identify with the body; they do not exist for the Ātma. Only he who has escaped their afflictions is fit for Mokṣa,” so he declared.
The first chapter, which gave these teachings, is called “Arjuna Viṣāda Yoga.” This chapter is like the foundation of the mansion of the Bhagavad Gītā. Only if the foundation is secure will the building stand secure. This Gītā mansion was raised five thousand years ago and still stands unshaken today; from that, each of us may ponder for himself how secure its foundation is, and what manner of master-builder laid it.