Chapter 2,Verse 31

svadharmam api chavekhya
na vikampitum arhasi
dharmyaad dhi yuddhaac chreyo'nyat
katriyasya na vidyate

Beginning from verse 31,Krishna start to analyze Arjuna's problems from the ethical point of view(Dharmic drishti),if,in case Arjuna could not comprehend the spiritual angle(Adhyatmika drishti).
He says that if the Mahabharatha was an immoral(adharmic) war,then taking part in it would definitly give you(Arjuna) papa,and you shall be destined for naraka.Hence,you should be afraid of it.Krishna wants to establish that this is a legitimate(dharma yudham) war and says that taking part in it would never be immoral.As a matter of fact,it is the duty of a kshatriya to fight adharmic people.And doing ones duty is never immoral.On the contrary,shying away from your duty as a kshatriya would give you papa and you shall be destined for naraka.

Here,Krishna agrees that war involves violence.And there is a general law that violence is unethical and non-violence alone is dharma.Dharma shastra talks about two types of dharma-
1.Samanya Dharma
2.Vishesha Dharma

Samanya dharma is the general rule that violence is evil.
But Dharma Shastra says that,even though the general rule is that violence is evil and should be avoided by all,there are circumstances where violence becomes a necessary evil,which becomes the duty of certain people at certain times.This is Vishesha dharma.


For example,when a jury has to pass a judgement,and has found the accused guilty,they must hand out a punishment,which is violence.They cannot sit back and say that they shall practice non-violence and thereby release the accused.

Taking this a step further,the supreme judge is the Bhagavan,an as an impartial judge,must hand out punya-phalam and papa-phalam to people depending on our actions.When handing out papa-phalam,Bhagavan himself is practicing violence as a necessary evil,since he is a "Karma-phala datha".

Hence,non-violence is samanya dharma and non-violence as a necessary evil becmes visesha dharma.At that time,talking of non-violence is wrong.Misplaced non-violence is adharma,in fact,it is as adarmic as violence itself.
It is with these that Arjuna has got confused with.In Mahabharatha,visesha dharma applies since it is a dharmic war,and to Arjuna,who is a kshatriya,restoring dharma is a duty.He confuses these because of his emotional attachment to his relatives.

Krishna wants to distinguish between samanya dharma & visesha dharma.Mahabharatha is an ethical war from the standpoint of visesha dharma,because Dhuryodhana had committed the "pancha maha papams",which by itself is a great accomplishment.Hence,he must be out in place.For this,Mahabharatha becomes necessary.

Being the brother of Dharma putra,Arjuna has become confused with the Dharma-shastra.
Krishna points this out.Hence he says that Arjuna cannot waver from doing his duty of fighting the Mahabharatha.Kshatriya means a person who rids the society of adharma.This is derived from the word "Kshatam",meaning disharmony.Hence,he who rids the society of disharmony is a kshatriya.
Hence,he says that fighting a righteous war to save the society becomes the primary duty of Arjuna and he must not run away from it.