Personality or self is no doubt centered in the physical organism. But there are valid grounds for believing that it is not identical with the body. That man is something more than his physical self, can easily be seen from the fact that whereas his body is continually changing, both in its inner structure as well as in its outward appearance, his self remains unchanged. What, then, is his real self? The answer is, the ego or "I" of whose real nature we know nothing except in so far as it expresses itself in its behavior or activities which are mediated by the body. Biology tells us that the human body is an organic structure, composed of millions of living cells which are continually changing. The moment a cell passes out of existence, it is replaced by a new one. In technical language, the process of catabolism is counterbalanced by the process of anabolism. Disintegration is quickly followed by re-integration. As a result of this, new cells are being produced and taking the place of older ones. Destruction and construction go side by side. The human body is, therefore, continually changing into a new one, so much so that it does not take more than three years, or seven as some believe, to renew itself completely. Now, if by "self" we mean the physical self, namely, the body which undergoes a complete change after every period of three or seven years, it necessarily follows that the individual too ceases to exist as often as his body does so. However improbable it may be, if man is equated with his body the conclusion is inescapable that he changes into a new individual every three or seven years. The practical consequences of such a view can be easily imagined.
Suppose A lends £10 to B. Consider that ‘A’ being a friend of ‘B’ waits patiently for several years, hoping that ‘B’ will pay back the money as soon as it is convenient for him to do so. When ‘A’ thinks that he had waited long enough, he demands payment. B, however, tells him that the two individuals between whom the said transaction took place have ceased to exist. A may insist that he remembers the transaction and that B is the same person who borrowed the money, but ‘B’ may emphatically maintain that he himself is not the person who borrowed the money and so is under no obligation to pay it back. It is obvious that if by "self" we mean the physical self, such absurd conclusions are inescapable. However seriously the scientist may assert that the physical self is transformed in a short period of time and hence we are not responsible for what we did before that period, nobody, not even the scientist himself, can accept this as a right principle of conduct. For, however the body may change; our personal identity is not affected thereby. We continue to be the same till the time of our death. The physical self, the body, might change but not the real self, the ego or the "I" which make me what I am.
The human self has the capacity to develop itself on the model of the Divine attributes. It then rises higher and higher in the scale of existence. It is a hard task and man should be perpetually on his guard against all that threatens, from within or without, to weaken and emasculate his self. Only the strong self can forge ahead towards the goal of self-realization.
A weak self can easily deviate from the right path. The restrictions which the Quran imposes on the individual are not designed to curb his freedom but to strengthen him and to stiffen his resistance to destructive forces, so that he may form a strong character and build up an enduring personality. Men of weak character often make good resolutions but seldom carry them out. The discipline of the Quranic way of life is intended to strengthen the self, so that it may successfully resist all forces which threaten its integrity, and remain steadfast in the pursuit of the good. In Holy Quran it is said that; People who proclaim that Allah Almighty alone is their Rabb (nourisher) and remain firm and steadfast in their commitment so much so that no power on earth can influence them otherwise, then the Malaika (the heavenly forces) will descend upon them (and strengthen them further - 33:43). The Malaika will say that have no fear, apprehension or grief but rejoice and receive the happy news of the blissful life of heavenly society that has been promised to you". (41:30)
Discipline hardens the ego. Rebuffs and disappointment call forth the best in it. Obstacles spur it on to more vigorous efforts. Such strong personalities can never suffer dissolution.