For the sense-bound the body may be just an instrument of sense enjoyment, but for the discriminating it is a vehicle for getting rid of worldliness and realizing our true, divine nature with the help of spiritual disciplines. ‘The body is primarily an instrument for the practice of dharma,’ goes the well-known saying. Thus the body deserves to be taken care of even as a vehicle is properly maintained to serve its purpose. The Katha Upanishad compares the human body to a chariot in which dwells the individual soul. Proper nutrition and regular exercise help the body remain fit for spiritual practice, whatever be our path: karma yoga (selfless work), jnana yoga (discrimination), raja yoga (mind control) or bhakti yoga (devotion). A spiritual aspirant takes care of his body and undergoes treatment for his ailments so that his body continues to be a fit instrument for spiritual practice and service to others, rather than being a burden to anyone.
The connection between the body and the mind is so subtle that they have strong mutual influence on each other. According to Vedanta, we are primarily souls, but have put on a subtle body and a gross body. That we have a subtle body is evident from our dreams: then we are able to perceive through our five senses even when the body and external senses are inactive. The subtle body is composed of our mind, buddhi, prana and subtle sense organs. In deep sleep we are detached from the subtle body also and remain one with ignorance covering the Atman.
Successful detachment from the body is a result of a strong will power, a strong, purified will that could detach itself from the body-mind complex and root itself in the Atman, the divine core behind them. Will being the dynamic aspect of buddhi, strengthening it means awakening the buddhi and directing it towards the Atman, which is what spiritual disciplines are about.
The soul is the master of the chariot, buddhi (discriminative faculty) is the charioteer, manas (mind, the deliberative faculty) is comparable to the reins, and the sense organs to the horses. The Upanishad stresses the need to rein in the horses so that the master could reach his destination. But this reining in needs to be done by the charioteer, who needs to be wide awake all the time; he cannot afford to be sleepy or sloppy. Unbroken horses and a sleeping charioteer can only spell disaster for the master. Controlled senses and a wide awake buddhi help one reach the goal of human life, which is God-realization or Self-realization.