The Hindu hell is temporary, of course, and very easy to enter. According to the key last shloka of Canto XVI, 'Hell has three gates -- lust, anger, and greed (kama, krodha, lobha).' For the sake of his atman, Arjuna is advised to give up all three.
After the magnificent epiphany of the Wishing Tree symbol, the sermonising of Canto XVI may seem a bit of an anti-climax. There is, however, a practical reason for the long, meticulous detailing of the divine nature and the anti-diving nature. Arjuna must have started wondering if there is for him any hope at of attaining the Highest Purusha. The high-flying ethical idealism and luxuriant smbology might appear to be outside the ken of a Kshatriya.
Not so, suggests Krishna. The caste system, to which Krisha has referred earlier, is well and fine -- and not so well and fine. The three gunas are useful aids. The three Purushas are splendid philosophical constructs -- and not so splendid too.
What really matters is whether a person is well meaning or not. This is the ultimate, and only significant, distinction. Am I a deva or asura, divine or anti-divine ? Am I seriously motivated, constructively inclined; or am I aggressive, flippant, negative ? It is not difficult to find that out, because that classification cuts across guna, caste, creed and race. So, Krishna's message of goodwill and hope : 'Divine birth leads to moksha, anti-divine to bondage. Do not worry, Arjuna, your birth is divine.'