The Webster Dictionary defines free will as:
1: voluntary choice or decision, I do this of my own free will.
2: freedom of humans to make choices that are not determined by prior causes or by divine intervention.
When theists are presented with a dilemma such as trying to explain why their God would allow terrible things to happen if he is all loving and all powerful, their go-to response is “free will.” This is not only a cop-out but not even an acceptable answer. A theist cannot truly believe they have free will while at the same time believing God knows their every thought and action.
If God knows what you are going to do before you do it, that would mean it is predestined. It is something that is going to happen and you have no choice in the matter. It does not matter that you have the option of changing your mind, because, in the end, God would still know what your final decision would be. Even if you were to change your mind 1000 times, God would still know what your final decision would be. If God knew yesterday that today you would eat cereal for breakfast, are you free to not eat cereal today? The problem is of course if you are free to not eat cereal today, God would have been wrong in knowing that you would eat cereal today.
If someone knows in advance what you will do, you do not have free will because it was decided ahead of time what you were going to do. Although you might have convinced yourself that you had free will in your decision, you did not because God knew before you did what you were going to decide.
Either we truly have free will and God (or anyone else) does not know what we will do tomorrow, or we do not and our future has already been decided and you are just playing out a role that had already been predetermined.