Krishna completes the argument. If even those considered lowly by society can reach the supreme goal through devotion, then what of virtuous brahmins and devoted rajarshis? For them, the path is that much more natural.
Then Krishna makes his personal appeal to Arjuna: 'Anityam asukham lokam imam prapya bhajasva mam.' Having been born into this world — which is impermanent and without lasting joy — devote yourself to me. It is not a command. It is an invitation from a friend who sees the full picture.
The words 'anityam asukham' are not pessimism. They are a diagnosis. A doctor who tells you the truth about your condition is not being negative — they are giving you the information you need to heal. Krishna describes the world accurately so that Arjuna can choose wisely.