The idea is that, as described in the śāstra, who is a brāhmaṇa, who is a śūdra, who is a kṣatriya, who is a vaiśya . . . It is all described in the Bhagavad-gītā. So satyaṁ śamo damas titikṣā ārjavam, jñānaṁ vijñānam āstikyaṁ brahma-karma svabhāva-jam (BG 18.42). Karma. Guṇa and karma. Here Aśvatthāmā, although he's born of a brāhmaṇa father, he did not possess the quality of a brāhmaṇa, neither the work of a brāhmaṇa. He degraded himself. First of all, he was engaged as a soldier to assist, to flatter Duryodhana. He wanted to please Duryodhana by killing the Pāṇḍavas. But he was such a fool, instead of killing the Pāṇḍavas, he killed the five sleeping sons of the Pāṇḍavas. How much abominable he is, just imagine. Here it is said, suptān avadhīn niśi bālakān. First of all, they were minor aged, and they were sleeping, and they were killed at night. Just see what kind of brāhmaṇa he is. A brāhmaṇa's business is not to kill. Even brāhmaṇa can kill, he doesn't require even sword or any other weapon. Simply by cursing he can kill—brāhmaṇa was so powerful. But still, it is not the business of a brāhmaṇa. When killing is required, it is done by the kṣatriyas, not by the brāhmaṇas.
Just like Viśvāmitra Muni, he was disturbed by the Tāḍakā rākṣasī. He was quite powerful. Even by cursing he could kill this Tāḍakā rākṣasī in the forest, but he did not do so. For killing the rākṣasī he approached Mahārāja Daśaratha. Because he is kṣatriya, he is the king, his business is to give protection to the disturbed citizens. Just like we apply to the magistrate, similarly the king is responsible. So he did not kill. Viśvāmitra formerly was kṣatriya, but since he became brāhmaṇa . . . By his endeavor in lifetime, he became a brāhmaṇa, a great sage, ṛṣi. So since he became brāhmaṇa, he was not interested in killing anyone. That is not brāhmaṇa's business. Brāhmaṇa's business is śamo damas titikṣā. Even if he is disturbed by somebody, titikṣā, he tolerates. Kāma-rūpa-tapasvin. He does not become . . . And when it is intolerable, he approaches the kṣatriya.So in considering all angles of vision, this Aśvatthāmā was not a brāhmaṇa. Therefore Kṛṣṇa personally advised him, mā enaṁ pārtha arhasi trātum: "Don't excuse him. Kill him, this brahma-bandhu. He has done wrong; now he deserves to be killed." It is clearly said. So does it mean that Kṛṣṇa is advising brahma-hatyā? No. Kṛṣṇa cannot do that. He is the teacher, world teacher. How He can advise somebody, especially His friend Arjuna? Bhakto 'si priyo 'si me (BG 4.3). Can you advise anything adversely to your friend? To your son? No. I must give very good advice. So Kṛṣṇa is advising Arjuna, "Don't excuse this rascal brahma-bandhu. Don't excuse." This is Kṛṣṇa's advice. But it does not mean that we can do anything and everything under the pretext of Kṛṣṇa's advice. No. You must be first of all a confidential friend or servant of Kṛṣṇa. You must receive direct order from Kṛṣṇa. Then you can do it. Otherwise not. Otherwise not. Under the pretext that "Kṛṣṇa said," "My spiritual master has said," "Prabhupāda has said," we manufacture something. Don't do that. Unless you are directly ordered, you cannot do at least such things as to chastise a brahma-bandhu. This should not be done. Here is direct order.