Vivekachudamani 338

देहादिसंसक्तिमतो न मुक्तिः 

मुक्तस्य देहाद्यभिमत्यभावः । 

सुप्तस्य नो जागरणं न जाग्रतः 

स्वप्नस्तयोर्भिन्नगुणाश्रयत्वात् ॥ ३३७ ॥ 

dehādisaṃsaktimato na muktiḥ 

muktasya dehādyabhimatyabhāvaḥ | 

suptasya no jāgaraṇaṃ na jāgrataḥ 

svapnastayorbhinnaguṇāśrayatvāt | 

(Sankaracarya's Vivekachudamani 338) 

There is no liberation for the one who is attached to the body etc., and the liberated person has no identification with the body, etc. One who is sleep is not awake, and one who is awake does not dream, for these two are opposite in nature. 

Just try to understand the difference between a living man and a dead body. As soon as the living force within the body is gone, then it is dead matter, useless. And so long the living force is there, the body is very important. As we experience in this body, there is something as dead matter and something as a living force, Similarly, there are two worlds: the material world and the spiritual world. We living entities belong to the spiritual world. We do not belong to the material world. Somehow or other, we are now in contact with this material world and material body, and therefore, although we are eternal living force, on account of our contact with this material body, we have to undergo four tribulations: birth, old age, disease, and death. In this material world, we get one type of body and it ends at a certain stage, just like any material thing. Take for example your dress. You dress in a garment, but when it is worn out and no longer usable, then you throw it and get another dress. Similarly, this material body is the dress of the spirit or living force. But because we are attached to this material world and we want to enjoy it, therefore we get different types of bodies. This body is explained in the Bhagavad-gita as a machine: Those who attached to this body will never gain liberation. Those who are interested in liberation will not waste time with material attachments.