Are teaching on gratitude and "duty" nessesary?
Teaching on gratitude &amp; “duty” is not necessary for Nibbana. MN 117 states gratitude &amp; duty is a defiled (asava) right view with attachment (upadhi) siding with merit. In MN 56, Upali's stream-entry resulted in independence from the teacher. In the Vakkali Sutta, Vakkali was rebuked for wrong gratitude. Dhammapada 294 states to "kill the mother &amp; father to attain Nibbana". In MN 86, the arahant Angulimala, ate his alms food without debt (obligation). Gratitude is a moral teaching for worldlings (puthujjana) but is unrelated to the goal of Buddhism, namely, Nibbana. Dhp 43 says:


  Na taṃ mātā pitā kayirā, aññe vāpi ca ñātakā; sammāpaṇihitaṃ cittaṃ, seyyaso naṃ tato kare
  
  Neither mother, father, nor any other relative can do greater good than the well-directed mind.