प्रतिपदमहमादयो विभिन्नाःक्षणपरिणामितया विकारिणस्ते ।न परिणतिरमुष्य निष्कलत्वा -दयमविकार्यत एव नित्य आत्मा ॥ ६१५ ॥
In plain words
At every instant the 'I' and everything that follows it come up different; they shift from moment to moment, so they are modifications, nothing more. This one does not transform. It has no parts, and what has no parts has nothing in it to change. So the Self is unalterable, and for that very reason, eternal.
Close to the Sanskrit
At every step the 'I' and the rest are various; by reason of transforming moment by moment, they are subject to modification. Of this one there is no transformation, because of partlessness; therefore this Self is precisely unmodifiable and eternal.