kim — what; indreṇa — with Indra; iha — here; bhūtānām — for living entities; sva-sva — each their own; karma — of fruitive action; anuvartinām — who are experiencing the consequences; anīśena — (Indra) who is incapable; anyathā — otherwise; kartum — to make; svabhāva — by their conditioned natures; vihitam — that which is ordained; nṛṇām — for men.
Living beings in this world are forced to experience the consequences of their own particular previous work. Since Lord Indra cannot in any way change the destiny of human beings, which is born of their own nature, why should people worship him?
Lord Kṛṣṇa’s argument here is not a negation of free will. If one accepts the existence of karma as a system of laws awarding reactions for our present activities, then we ourselves, according to our nature, will decide our future. Our happiness and distress in this life have already been adjudicated and fixed according to our previous activities, and not even the demigods can change that. They must award us the prosperity or poverty, sickness or health, happiness or distress due us by our previous work. However, we still retain the freedom to select a pious or impious mode of activity in this life, and the choice we make will determine our future suffering and enjoyment.
For example, if I was pious in my last life, in this life the demigods may award me great material wealth. But I am free to spend my riches for good or for bad purposes, and my choice will determine my future life. Thus, although no one can change the karmic results due him in this life, everyone still retains his free will, by which he determines what his future situation will be. Lord Kṛṣṇa’s argument here is quite interesting; however, it neglects the overriding consideration that we are all eternal servants of God and must satisfy Him by all that we do.