The law of change is explained in the 16th verse of Chapter 2 of the Bhagavad Gita ----
[ नासतो विद्यते भावो नाभावो विद्यते सतः । उभयोरपि दृष्टोऽन्तस्त्वनयोस्तत्त्वदर्शिभिः ॥१६॥ ]
There is no being in the unreal, and there is no being in the real. The end of both has been seen by the seers of the truth.
There is no permanence in the changing body. Modern medical science has also accepted that the body keeps changing every moment due to the action and reaction of various cells. In this way the body keeps growing and aging, but despite the constant changes in the body and mind, the soul remains permanent. This is the difference between the body and the soul. The body is ever changing and the soul is immortal and eternal.
In chapter 2, chapter 13 it is mentioned that ----
[ देहिनोऽस्मिन्यथा देहे कौमारं यौवनं जरा । तथा देहान्तरप्राप्तिर्धीरस्तत्र न मुह्यति ॥१३॥ ]
In this body of the embodied, childhood, youth and old age are all the same. Thus the steadfast does not become deluded by the attainment of another body.
The soul itself remains immortal, but the body is constantly going into death. As soon as the soul enters the womb, this sequence of death begins. When the pregnancy ends, then childhood comes, when childhood dies, then youth comes, when youth dies, then old age comes, when old age dies, then the state of death comes, that is, the second birth is attained. In this way the states of the body change, but the soul living in it remains the same. The reason is that the parts of the body and the soul living in it are different, hence man should never consider himself as the body, the liberation from bondage is of the self, not of the body.
All the circumstances of the world are of coming and going, meeting and separation. Man wants that the pleasant situation should remain and the painful situation should not come, but the pleasant situation always goes away and the painful situation always comes. This is the natural law or the auspicious law of God. Therefore, man should accept every situation happily. It is a mistake to see stability in things which are constantly changing. This mistake gives rise to attachment and desire. It is the mistake of man to consider the body which is coming together and going away as I, mine and mine. This mistake is not natural, but is artificial, created by man. Therefore, man himself will have to try to correct this mistake.
Questionnaire -
1) What is the meaning of the law of change created by God?
2) How has science explained the law of change?
3) Why does a person get disturbed by changes in his life?
4) What is the difference between body and soul?
5) How does the state of the body change?