“Yes — the one who waged war his whole life long and conquered the entire earth, and then renounced his kingdom in order to rest.”
Arjuna, do you know of Emperor Muchukunda, the son of Emperor Mandhata? Yes — the one who waged war his whole life long and conquered the entire earth, and then renounced his kingdom in order to rest. Arjuna, wondrous is the one who comes to know that the world is toil, and that austerity (tapasya) is the only rest.
Chapter 20 of 35 — a single teaching, 1 min in total.
The Mahabharata is less a story with a moral than a very long argument about how to act. Its characters are given impossible situations and are judged not on the outcome but on the quality of their reasoning and the honesty of their motives.
Krishna's role throughout is the counsellor who refuses easy answers. He does not remove the difficulty; he changes what the person is able to bring to it.