Kural - 682

Love, knowledge, power of chosen words, three things,
Should he possess who speaks the words of kings

Explanation
Love (to his sovereign), knowledge (of his affairs), and a discriminating power of speech (before other sovereigns) are the three sine qua non qualifications of an ambassador.

Tamil Transliteration
Anparivu Aaraaindha Solvanmai Thoodhuraippaarkku
Indri Yamaiyaadha Moondru.