rationalfrummie
1. If Hashem knows what decisions we will make in the future and how our lives will turn out, how can He reward us or punish us– we are merely doing what he knew we would do all along!
He knew we would do it potentially but we get reward for doing it because WE did it. The act makes it ours. Otherwise there would only be reward for potential good and that would be nehama dikesufa “bread of embarrassment/shame.” (the following parenthtical sentences are from Rabbi Rosenfeld on Torah.org: If G-d were to “reward” us for doing nothing it would not be reward; it would be humiliation. Receiving a handout is an embarrassing, mortifying experience. Getting something we did not earn does not make us feel good about ourselves. It makes us feel crushed, ashamed to show our faces in public. Try looking in the face of someone who did you an enormous favor. You’d much rather never have to see him again. If G-d were to give us what we did not earn, we would hardly feel “close” to Him. We would never be able to have any kind of meaningful relationship with G-d in the World to Come — which is really what the World to Come is all about.) True He knows what we will do but He doesnt make us do it. You chose (using your will or ratzon) to do every mitzva you did.
2. Also, how does this fit in with the idea that harsh gezeiros can be overturned- does that mean that the future isn’t set, even if Hashem planned it out from creation?
Hashem has rules set up for how the world works. If abc happens then def will happen. However built into that system there are certain ways to circumvent certain occurrences. Like through tefillah or certain tremendous deeds. Yes Hashem knows how everything will end up but like others have told you that has no bearing on your choices.
3. Also, what about the idea that our futures are set on Rosh Hashnah? Does that mean Hashem didn’t know what would happen to us the year before, next year?
Hashem knows everything always but maybe you can say it is all like the way you can have an idea and know what you want to do but that doesnt make it done just yet. I think what happens on Rosh Hashanah is that Hashem writes down and puts into motion the power to make that year the way its supposed to go based on your merit. He knew it before and knew what He would write before but now He makes it happen so to speak and sets the ball in motion.
I hope this helps you.