तेषामन्तावसायिनोऽप्यवध्याः किमङ्ग पुनर्ब्राह्मणाः ॥ कZ_०१.१६.१५ ॥
teṣām antāvasāyino 'py avadhyāḥ kim aṅga punar brāhmaṇāḥ
Among them, even envoys of lowly origin are not to be slain—how much more so, then, Brahmin envoys.
To strengthen the rule of inviolability by stating it applies universally, and is even more compelling when the envoy holds a revered social-religious status.
To preserve communication channels and reduce escalation by protecting diplomatic intermediaries.