The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
27. But on account of twofold designation, (the relation of the highest Self to the individual soul has to be viewed) like that of the snake to its coils.
In order to justify his own view as to the relation of the conciliating individual soul and the conciliated highest Self, the Sûtrakâra mentions a different view of the same matter.--Some scriptural passages refer to the highest Self and the individual soul as distinct entities, cp. e.g. Mu. Up. III, 1, 8,' Then he sees him meditating on him as without parts,' where the highest Self appears as the object of the soul's vision and meditation; Mu. Up. III, 2, 8, 'He goes to the divine Person who is greater than the great;' and 'Bri. Up. III, 7, 15, 'Who rules all beings within;' in which passages the highest Self is represented as the object of approach and as the ruler of the individual soul. In other places again the two are spoken of as non-different, so e.g. Kh. Up. VI, 8, 7, 'Thou art that;' Bri. Up. I, 4, 10, 'I am Brahman;' Bri. Up. III, 4, 1, 'This is thy Self who is within all;' Bri. Up. III, 7, 15, 'He is thy Self, the ruler within, the immortal.'--As thus difference and non-difference are equally vouched for by scripture, the acceptation of absolute non-difference would render futile all those
texts which speak of difference. We therefore look on the relation of the highest Self and the soul as analogous to that of the snake and its coils. Viewed as a whole the snake is one, non-different, while an element of difference appears if we view it with regard to its coils, hood, erect posture and so on.