Astronomical calculations of stellar influences upon a living being are not suppositions, but are factual, as confirmed in Śrīmad-Bhāgavatam. Every living being is controlled by the laws of nature at every minute, just as a citizen is controlled by the influence of the state. The state laws are grossly observed, but the laws of material nature, being subtle to our gross understanding, cannot be experienced grossly. As stated in the Bhagavad-gītā (3.9), every action of life produces another reaction, which is binding upon us, and only those who are acting on behalf of Yajña (Viṣṇu) are not bound by reactions. Our actions are judged by the higher authorities, the agents of the Lord, and thus we are awarded bodies according to our activities. The law of nature is so subtle that every part of our body is influenced by the respective stars, and a living being obtains his working body to fulfill his terms of imprisonment by the manipulation of such astronomical influence. A man’s destiny is therefore ascertained by the birthtime constellation of stars, and a factual horoscope is made by a learned astrologer. It is a great science, and misuse of a science does not make it useless. Mahārāja Parīkṣit or even the Personality of Godhead appear in certain constellations of good stars, and thus the influence is exerted upon the body thus born at an auspicious moment.
This suitable arrangement of astral influences is never a creation of man’s will, but is the arrangement of the superior management of the agency of the Supreme Lord. Of course, the arrangement is made according to the good or bad deeds of the living being. Herein lies the importance of pious acts performed by the living being. Only by pious acts can one be allowed to get good wealth, good education and beautiful features.
– excerpted from his commentary on Srimad Bhagavatam 1.12.12