narake niyataṁ vāso
Arjuna bases his argument not on his own personal experience, but on what he has heard from the authorities. That is the way of receiving real knowledge. One cannot reach the real point of factual knowledge without being helped by the right person who is already established in that knowledge. There is a system in the varṇāśrama institution by which before death one has to undergo the process of atonement for his sinful activities. One who is always engaged in sinful activities must utilize the process of atonement, called prāyaścitta. Without doing so, one surely will be transferred to hellish planets to undergo miserable lives as the result of sinful activities.