Bhagavad Gita

ಅಥ ಚೇತ್ ತ್ವಂ ಧರ್ಮ್ಯಮಿಮಂ ಸಂಗ್ರಾಮಂ ನ ಕರಿಷ್ಯಸಿ ।
ತತಃ ಸ್ವಧರ್ಮಂ ಕೀರ್ತಿಂ ಚ ಹಿತ್ವಾ ಪಾಪಮವಾಪ್ಸ್ಯಸಿ ॥೩೩॥
atha cet tvaṃ dharmyamimaṃ saṃgrāmaṃ na kariṣyasi |
tataḥ svadharmaṃ kīrtiṃ ca hitvā pāpamavāpsyasi ||33||

Gist of the sloka:
If you do not do your solemn duty when the opportunity has presented itself, you will incur sin [of not following the Sanathana dharma thereby displeasing the Lord] and will be cursed.
Lord Krishna is telling Arjuna, in case you are worried of accumulating sins by fighting the war, then by not going to the war, you are going to accumulate even greater sins and the gates of the Hell would be opened for you.
This is a dharmic war [reestablishing the rule of dharma]. If you enter the fight, you would be on the good side fighting for righteousness. If you stay out, then you would be working against the Sanathana dharma, Kula dharma and induvial dharma.
This non-action would be blemish on your character forever along with accumulating great sins. Lord Krishna is trying to educate Arjuna about the real dharma and how and why one’s actions should be in alignment with it.
Lord Krishna is giving the criteria for distinguishing between ‘punya’ and ‘papha’ [non-meritorious deed].
Telling truth is one of the aspects of Sanathana dharma. Let us see an example. A pious person with some valuables is running away from dacoits in a forest. He sees a hermitage and sneaks inside it and stays hidden. The hermitage person sees this scene. Dacoits arrive at the scene and asks this hermitage person if he has seen the person with the valuables.
In case he tells the dacoits, that the person is inside the hermitage, the dacoits would not only steal the valuables but might also harm the pious person. Telling the info as is, might be considered telling truth. In case, he misguides the dacoits and makes them go away in a different direction, he can only do so when he lies.
The question would be what is the actual truth here. Lord says by saying a small lie to protect a pious person is the ‘truth’ and by telling the actual info causing harm to the person is ‘falsehood’. The context being the dacoits are not ‘pious’ people and their intention is to cause harm and steal. To encourage such evil is ‘falsehood’ and to prevent such event is ‘truth’. Balance between small lie to protect pious against real info encouraging evil.
Similar is the situation when a person puts knife into a person body. The context behind the action determines the ‘punya’ and ‘papha’ of the action. One might be a surgeon another a thief.