(Click to enlarge painting of Lord Krishna controlling the demigods)
"Concerning your debate with the professor who claims that if God knows everything then His foreknowing makes men very much like puppets or machines.
Persons who think of God like himself has no knowledge of God. He immediately becomes a mudha, fool rascal. Avajananti mam mudha (BG 9.11) . . . God is omniscient and omnipotent. He knows everything what is going to happen. Therefore to save the living entity from future calamity He says, sarva dharman parityajya mam ekam saranam vraja (BG 18.66). . . So although He knows what is going to happen in the future, He can cancel all that was going to happen by His Grace, that is God's omnipotency. For a devotee, the future destiny is changed as confirmed in the Brahma-samhita:
yas tvindra-gopam athavendram aho sva-karma-
karmapi nirdhahati kintu ca bhakti-bhajam
govindam adi-purusam tam aham bhajami
'Let me offer my respectful obeisances unto the original Personality of Godhead, Govinda, Who regulated the sufferings and enjoyments of fruitive activity for everyone—from the heavenly King Indra down to the smallest insect (indra-gopa). That very Personality of Godhead destroys the fruitive karma of one engaged in devotional service.'
So anyone who surrenders to Krishna, his destiny is changed by the omnipotency of God. He takes charge of the devotee and guides him how the devotee can go back to Home, Back-to-Godhead. This is the Mercy of God. He knows everything and still He says 'sarva dharman parityajya mam ekam saranam braja . . . (BG 18.66)' But, you are thinking God like you, what is destined is going to happen and even God cannot change it? Then God is impotent? This is their version, not God's. God says surrender to Me and I shall cancel all your destiny, aham tvam sarva papebhyo moksayisyami ma sucah . . . God will save you from the destiny that you have created by misuse of your independence. He knows but still He is so kind. Surrender has nothing to do with your destiny, that will depend on you (the spirit-soul) because you have a little independence, a little freedom.
Theirs is atheistic argument. God is not only omniscient, but also Almighty. Predestiny is there but it is cancelled if you surrender to Him, otherwise God is not the controller. Theirs is like karma mimamsa philosophy, that God is our servant and He must reward me according to my activities. If you surrender to Krishna there is no more predestiny. He knows if you do this you must suffer, so why do you suffer. You take His advice. Even if he says predestined, so why don't you surrender to Krishna now, and get out of this material condition."
(Srila Prabhupada Letter, October 21, 1975)