Chapter1- Ślokās 35*,*36
api trailokya rājyasya hetoḥ kiṃ nu mahīkṛte || 35 ||
nihatya dhārtarāṣṭrān naḥ kā prītiḥ syāj-janārdana |
(1.35*-*1.36)
janārdana- O Janārdana!, kā prītiḥ- what pleasure; syāt- will be there; naḥ- for us; nihatya- by killing; dhārtarāṣṭrān- the sons of Dhṛtarāṣṭra; trailokya rājyasya api hetoḥ- for gaining sovereignty over the 3 worlds; kiṃ nu- what to speak of; mahīkṛte- this earth alone;
Purport
“I am not prepared to slay them even in exchange for sovereignty over the three worlds, what to speak of this earth alone. O Janārdana! What pleasure will we derive on killing these sons of Dhṛtarāṣṭra.”
Janārdana rakṣāpratipakṣān janān anapekṣaḥ ardayatīti janārdanaḥ Sahasranāmabhāṣyaṃ 128 (Janārdana is the one who attacks the jana (people) who are opposed to a person's safety even without the person's expectation to be protected). The derivation for the word 'Janārdana' is dasyutrāṇāt janārdanaḥ. Thus, Bhagawān is called Janārdana as HE does not spare the opponents of HIS dear ones. Arjuna wished to fortify his belief that one should not cause harm to his own loved ones. He therefore addressed Kṛṣṇa as Janārdana, to point out that while HE acquired the famed title 'Janārdana' for being the protector of HIS people from evil opponents, how could they perform the contrary act of causing harm to their own people?