The physical body needs to be maintained in a healthy state otherwise the power which pours in during spiritual experiences can lead to psycho-physical instabilities.
The Mother on physical culture
Physical culture is the process of infusing consciousness into the cells of the body. One may or may not know it, but it is a fact. When we concentrate to make our muscles move according to our will, when we endeavour to make our limbs more supple, to give them an agility, or a force, or a resistance, or a plasticity which they do not naturally possess, we infuse into the cells of the body a consciousness which was not there before, thus turning it into an increasingly homogeneous and receptive instrument, which progresses in and by its activities. This is the primary importance of physical culture. Of course, that is not the only thing that brings consciousness into the body, but it is something which acts in an overall way, and this is rare. I have already told you several times that the artist infuses a very great consciousness into his hands, as the intellectual does into his brain. But these are, as it were, local phenomena, whereas the action of physical culture is more general. And when one sees the absolutely marvellous results of this culture, when one observes the extent to which the body is capable of perfecting itself, one understands how useful this can be to the action of the psychic being which has entered into this material substance. For naturally, when it is in possession of an organised and harmonised instrument which is full of strength and suppleness and possibilities, its task is greatly facilitated.
(Collected Works of the Mother, vol 10, p 30)
Sri Aurobindo on the fitness required
The body is not only the necessary outer instrument of the physical part of action, but for the purposes of this life a base or pedestal also for all inner action. All working of mind or spirit has its vibration in the physical consciousness, records itself there in a kind of subordinate corporeal notation and communicates itself to the material world partly at least through the physical machine. But the body of man has natural limitations in this capacity which it imposes on the play of the higher parts of his being. And, secondly, it has a subconscient consciousness of its own in which it keeps with an obstinate fidelity the past habits and past nature of the mental and vital being and which automatically opposes and obstructs any very great upward change or at least prevents it from becoming a radical transformation of the whole nature. It is evident that if we are to have a free divine or spiritual and supramental action conducted by the force and fulfilling the character of a diviner energy, some fairly complete transformation must be effected in this outward character of the bodily nature. The physical being of man has always been felt by the seekers of perfection to be a great impediment and it has been the habit to turn from it with contempt, denial or aversion and a desire to suppress altogether or as far as may be the body and the physical life. But this cannot be the right method for the integral Yoga. The body is given us as one instrument necessary to the totality of our works and it is to be used, not neglected, hurt, suppressed or abolished. If it is imperfect, recalcitrant, obstinate, so are also the other members, the vital being, heart and mind and reason. It has like them to be changed and perfected and to undergo a transformation. As we must get ourselves a new life, new heart, new mind, so we have in a certain sense to build for ourselves a new body.
The first thing the will has to do with the body is to impose on it progressively a new habit of all its being, consciousness, force and outward and inward action. It must be taught an entire passivity in the hands first of the higher instruments, but eventually in the hands of the spirit and its controlling and informing Shakti. It must be accustomed not to impose its own limits on the nobler members, but to shape its action and its response to their demands, to develop, one might say, a higher notation, a higher scale of responses. At present the notation of the body and the physical consciousness has a very large determining power on the music made by this human harp of God; the notes we get from the spirit, from the psychic soul, from the greater life behind our physical life cannot come in freely, cannot develop their high, powerful and proper strain. This condition must be reversed; the body and the physical consciousness must develop the habit of admitting and shaping themselves to these higher strains and not they, but the nobler parts of the nature must determine the music of our life and being.
The control of the body and life by the mind and its thought and will is the first step towards this change. All Yoga implies the carrying of that control to a very high pitch. But afterwards the mind must itself give place to the spirit, to the spiritual force, the supermind and the supramental force. And finally the body must develop a perfect power to hold whatever force is brought into it by the spirit and to contain its action without spilling and wasting it or itself getting cracked. It must be capable of being filled and powerfully used by whatever intensity of spiritual or higher mind or life force without any part of the mechanical instrument being agitated, upset, broken or damaged by the inrush or pressure, – as the brain, vital health or moral nature are often injured in those who unwisely attempt Yogic practice without preparation or by undue means or rashly invite a power they are intellectually, vitally, morally unfit to bear, – and, thus filled, it must have the capacity to work normally, automatically, rightly according to the will of that spiritual or other now unusual agent without distorting, diminishing or mistranslating its intention and stress. This faculty of holding, dharana shakti, in the physical consciousness, energy and machinery is the most important siddhi or perfection of the body.
The result of these changes will be to make the body a perfect instrument of the spirit. The spiritual force will be able to do what it wills and as it wills in and through the body. It will be able to conduct an unlimited action of the mind or at a higher stage of the supermind without the body betraying the action by fatigue, incapacity, inaptitude or falsification. It will be able too to pour a full tide of the life-force into the body and conduct a large action and joy of the perfected vital being without that quarrel and disparity which is the relation of the normal life-instincts and life-impulses to the insufficient physical instrument they are obliged to use. And it will also be able to conduct a full action of the spiritualised psychic being not falsified, degraded or in any way marred by the lower instincts of the body and to use physical action and expression as a free notation of the higher psychical life. And in the body itself there will be a presence of a greatness of sustaining force, an abounding strength, energy and puissance of outgoing and managing force, a lightness, swiftness and adaptability of the nervous and physical being, a holding and responsive power in the whole physical machine and its driving springs [mahattva, bala, laghuta, dharana-samarthya] of which it is now even at its strongest and best incapable.
(Sri Aurobindo. Synthesis of Yoga, Chap XIV, Power of the Instruments)