For a kṣatriya who are engaged in fighting, in religious fight... Fight must be religious fight. The cause must be right. Then the fighting is all right. So kṣatriya killing in the religious fight, he's not responsible, he's not sinful. That is stated. Just like brāhmaṇa. He sacri... He puts in sacrifice some animal. That does not mean he's killing. Similarly, kṣatriya, when he's engaged in killing, he's not sinful. This will be explained in the next verse. "So it your duty. Don't be worried that you are killing your kinsmen or your grandfather. Take it from Me, assurance, that the dehī, avadhya, you cannot kill, he's eternal."
If a ksatriya engaged in his own occupation kills an enemy, there is no sin incurred
Bhagavad-gita As It Is
BG Chapters 13 - 18
One should act to satisfy the Supreme Lord. For example, Arjuna was a kṣatriya. He was hesitating to fight the other party. But if such fighting is performed for the sake of Kṛṣṇa, the Supreme Personality of Godhead, there need be no fear of degradation. In the business field also, sometimes a merchant has to tell so many lies to make a profit. If he does not do so, there can be no profit. Sometimes a merchant says, "Oh, my dear customer, for you I am making no profit," but one should know that without profit the merchant cannot exist. Therefore it should be taken as a simple lie if a merchant says that he is not making a profit. But the merchant should not think that because he is engaged in an occupation in which the telling of lies is compulsory, he should give up his profession and pursue the profession of a brāhmaṇa. That is not recommended. Whether one is a kṣatriya, a vaiśya, or a śūdra doesn't matter, if he serves, by his work, the Supreme Personality of Godhead. Even brāhmaṇas, who perform different types of sacrifice, sometimes must kill animals because sometimes animals are sacrificed in such ceremonies. Similarly, if a kṣatriya engaged in his own occupation kills an enemy, there is no sin incurred. In the Third Chapter these matters have been clearly and elaborately explained; every man should work for the purpose of Yajña, or for Viṣṇu, the Supreme Personality of Godhead. Anything done for personal sense gratification is a cause of bondage. The conclusion is that everyone should be engaged according to the particular mode of nature he has acquired, and he should decide to work only to serve the supreme cause of the Supreme Lord.
Bhagavad-gita As It Is Lectures
Bhīṣma was lying on the bed of arrows, preparing for his death. So Kṛṣṇa wanted that these Pāṇḍavas should go to Bhīṣma and hear his instruction. Therefore, despite His advice to Mahārāja Yudhiṣṭhira, that "There was no wrong on your part. You are thinking that you have killed, or for your sake so many men have been killed. That is not... You are not responsible for that. You are not sinful..." For a kṣatriya, killing is not sinful. For a brāhmaṇa, sacrificing an animal in the arena, that is not sinful. So it is all explained in the Bhagavad-gītā, sa doṣam api na tyajet (BG 18.48). Killing is bad, but a kṣatriya's business is to kill. Without killing, one cannot become perfect kṣatriya. Because he has to give protection, and there are so many demons, rascals. So if the king becomes nonviolent, how other citizens will be given protection? No.
So the king's business is as soon as he sees one undesirable element, immediately he would kill him. That is real protection. Just like when Parīkṣit Mahārāja was going on tour, he saw one black man was trying to kill a cow. Immediately saw, "Who are you? You are trying to kill cow in my kingdom? I shall kill you." He immediately took out his sword. This is king, that... Not that animals should not be given protection, only man should be given protection. No. Prajā. Prajā means one who taken birth in the kingdom. That is called prajā.
Personally, one should remain very humble and meek, but that does not mean that when there is... For a kṣatriya, to kill the enemies, that is dharma-yuddha. That is religious. Therefore there was section—kṣatriya section, the brāhmaṇa section, the vaiśya section—that everyone is engaged in his own occupational duty. So other section, brāhmaṇa, vaiśya, śūdras, if they are in difficulty, they should lodge complaint to the king. Just like in these days also, suppose one is wrong-doer. He has done wrong to me. I cannot take directly to punish him. No. That you cannot do. You have to lodge the complaint to the government agent, and if required, government can kill him, sanction, "Kill this man. He is a murderer." So the sanction should come from there. Similarly, these divisions, very scientific. Killing business is for the kṣatriya, not for the brāhmaṇas. Kṣatriya, he can kill; there is no sin for him. The brāhmaṇas are not going to kill.
So this system—brāhmaṇa, kṣatriya, vaiśya, śūdra—very scientific system. Cātur-varṇyaṁ mayā sṛṣṭaṁ guṇa-karma-vibhāgaśaḥ (BG 4.13). But now everything is lost. But to make people happy, the Vedic culture is the most perfect. The kṣatriyas are meant for fighting. Kṣatriyas are meant for ruling, punishing. These are meant for the kṣatriyas.