Bhagavad Gita Chapter 1 Sloka 33 (1.33)

ಯೇಷಾಮರ್ಥೇ ಕಾಂಕ್ಷಿತಂ ನೋ ರಾಜ್ಯಂ ಭೋಗಾಃ ಸುಖಾನಿ ಚ।
ತ ಇಮೇSವಸ್ಥಿತಾ ಯುದ್ಧೇ ಪ್ರಾಣಾಂಸ್ತ್ಯಕ್ತ್ವಾ ಧನಾನಿ ಚ ॥೩೩॥
yeṣāmarthe kāṃkṣitaṃ no rājyaṃ bhogāḥ sukhāni ca|
ta imeSvasthitā yuddhe prāṇāṃstyaktvā dhanāni ca ||33||
Sloka 1:33
Gist of the sloka:
For whose sake is this need for rulership? These people, throwing aside richness and kingdoms [properties] have stood for fight, because of expectation of rewards and comforts.
Explanation:
Even if one needed this rulership/kingdom, it would be for whose sake? After all we should be keeping our teachers, senior relatives happy and comfortable. Rather after killing them, how can we be happy?
For whose sake we were hoping to win the kingdom, they themselves have leaving aside all their possessions, desires and their lives, have aligned themselves to fight the war.