तꣳ होवाच यथा सोम्य महतोऽभ्याहितस्यैकोऽङ्गारः खद्योतमात्रः परिशिष्टःस्यात्तेन ततोऽपि न बहु दहेदेवꣳ सोम्यते षोडशानां कलानामेका कलातिशिष्टा
In plain words
The father said to him, 'Gentle one, suppose there is a huge pile of burning logs, and a single ember no larger than a firefly is left behind. With that little spark you could not burn much fuel on the earth. In the exact same way, gentle one, only a single sixteenth part of your mind now remains active in you.'
Close to the Sanskrit
To him he spoke: 'Just as, O gentle one, of a great burning [fire] a single ember, firefly-sized, might be left over, by that even [much] not it might burn, thus indeed, O gentle one, of your sixteen parts one part is remaining.'