यस्याग्निः शरीरं योऽग्निमन्तरो यमयत्येष त आत्मान्तर्याम्यमृतः ॥ ५ ॥
In plain words
Fire is his body; he governs fire from inside it. He is your self, the one who rules from within -- and he does not die.
Close to the Sanskrit
Whose body is fire, who controls fire from within -- he is your self, the inner controller, immortal.