In plain words
Advaitopāsana: Ādi Śaṅkara [taught]: In the cow's body there is milk; in that milk there is ghee. Even so, with that ghee [as it sits in the milk], the cow gains no strength. But milking that milk, boiling it, setting it with a starter, churning it, taking out the butter, clarifying it, and then making the cow drink that ghee again — then strength results. In that same way, though the Lord of all is indwelling in all, without the practices and means of sādhana he cannot bring about [his own] benefit in human beings. Just as oil [is present] in sesame seeds, butter in curd, water in the earth, and fire in wood, all remaining mingled [though hidden], the Indweller of all remains mingled in human beings' bodies and minds. To separate them out, effort and spiritual practice must be undertaken. Then the non-difference of those two — their non-duality — becomes known. That itself is Mokṣa.