For the born, for one who has gained birth, death is certain, unfailing; and birth is certain for the dead. Therefore this matter, marked by birth and death, cannot be turned aside; and in a matter that cannot be turned aside you should not grieve. Grief is not right even with regard to beings that are aggregates of effect and instrument; here is why.

For what has come to be, destruction is certain, found to be unavoidable; and likewise for what has been destroyed, birth is unavoidable. How is this found, that the destroyed comes to be? Because origination is apprehended only of the existent, and never of the non-existent. Origination, destruction, and the rest are particular states of an existent substance. Substances such as threads exist already, and, when joined with a particular arrangement, are called cloth and the like. Even one who upholds the doctrine that the effect does not pre-exist apprehends only this much, for there no substance other than the particular configuration of the threads is cognised. Since the particular dealings, the working of factors, the taking of a new name, and the rest are accounted for by just this much, it is not right to posit another substance. So origination, destruction, and the rest are particular states of an existent substance. When a substance that has come to the state called origination reaches another state contrary to it, that is called destruction. As with the substance clay and its succession of states, lump, pot, potsherd, powder, and so on, the succession of states of a substance subject to transformation cannot be avoided. There, the prior state's reaching of a later state is the destruction of the substance in the prior state, and that same is its origination in the later state. So the succession of states called origination and destruction is, for a substance subject to transformation, not to be set aside; therefore you ought not to grieve over it. Even the slighter grief that might come of seeing an existent substance reach a state contrary to its prior state does not hold of beings such as men. So the Lord says.

This is a brief sub-gloss. For a fuller reading of this verse, see Madhusūdana, Śaṅkara, or Rāmānuja above.

Why should there be no grief? Because birth and death are fixed and certain, Krishna says with 'for the born, death is sure'.