सत्यवादिन: truth speaking Dasaratha's, धर्मिष्ठम् च conforming to morality, यशस्यं च conducive to fame, वचनम् words, श्रुत्वा having listened, विदेहाधिपति: Janaka, परम् extreme, विस्मयम् admiration, आगत: filled with.

Janaka was filled with extreme admiration to hear one who was truthful, righteous and famous (this Dasaratha).