One of my Catechism class students asked me the question of how can God be all knowing - such that he knows what we will do or knows the future as well as the past and at the same time how can we have free will. From a 12 year old, that is a pretty deep question. Theologians have been debating that for centuries. Here is my feeble attempt at a reconciliation.
I affirm that God is all knowing and we have free will at the same time. I affirm that God knows the future and the past and the present equally well. I also affirm that we have the opportunity to choose our beliefs and our actions.
So, how can both be true.
I believe it is a question of perspective. As human beings, we live in "time." We tend to think of "eternity" as just a very long time or time without end. I believe that is wrong. To live in Eternity, is to live outside of time. All time is present in eternity. So, God knows what we will do tomorrow because He sees us doing it. So, to see things from God's perspective is to affirm predestination and what some call "fate" or "destiny." This causes some people to believe in a detrimistic universe - everything works toward a certain outcome that is predetermined.
If, however, we look at things from the human perspective, we have the choices in front of us. We have not yet arrived at "tomorrow," so no one knows what we will do or how we will react. So, we have free will.
How do we reconcile these two truths? When working with inmates, I often try to help them learn to make decisions by draw a "decision tree" where they try to chart out how they will respond with different options and then to think ahead to what those options will lead to. I don't chart the options for them, they make the chart. I don't make the decisions for them, they make the decisions, but they can see the outcomes of different decisions (granted, with a less than accurate picture of the outcome).
I think that in Eternity, God sees the options of all the myriad of decisions all the people in the universe makes and He sees the outcomes with perfect clarity. S0, let's take a simple example for explaination.
Say you want to go to dinner, but aren't sure at which restaurant to eat. You have a choice of 5 or 6 you like but aren't sure which one to pick. Before you go, God see you eating at all 5 or 6 places (and even the odd place you don't normally frequent). But, it has not yet happened until you actually pick a place. So, God knows the outcome and you still have free will.
I hope this helps us to reconcile free will and predestination.