गानस्येष्टे य एव विद्वान्साम गायतिसाम गायति ॥ ९ ॥
In plain words
He alone has mastery over the song who sings the Sāma chant with understanding, who sings the Sāma chant.
Close to the Sanskrit
He has power over the song who knowing sings the Sama chant, sings the Sama chant.