Good point.
Just as even God's omniscience does not negate free will. (It is sometimes claimed that because we have free will, God cannot be omniscient.)
But God is definitely omniscient, for in him is found all knowledge (Colossians 2:2b-3; 1 John 3:20b). He is able to declare the end from the beginning (Isaiah 46:10), and his foreknowledge is determinate (Acts 2:23, Revelation 1:1). But his omniscience coexists with his giving people free will. He still lets people choose for themselves what they are going to do (Joshua 24:15, Deuteronomy 30:19, Isaiah 1:19-20, Philemon 1:14).
An analogy for how people can have a meaningful free will and yet God can already know what they are going to choose to do, would be a symphony conductor who wanted to make a film of a "Free Will Symphony" which sounded good enough to show off to the world. So he told his symphony musicians his plan, set up a movie camera in front of them, and said that each of them could start playing whatever he or she wanted for an hour. But when they all started playing, it sounded awful for the entire hour. It was utter cacophony. So the conductor sent them home and told them to come back the next day and try again. The next day sounded worse than the first. And the day after that was also bad. This went on day after day for months, until one day the most amazing sound arose from the symphony, a congeries of all the different melodies and rhythms which was unlike anything that anyone had ever heard before. So the conductor kept the movie of that day, and showed it off to the world.
But when the symphony musicians began watching the movie at its world premiere, with all the most-famous musicians of the world seated around them in the theater, some of the symphony musicians began to squirm in their seats. For example, one of the bass players had happened to choose that day (the day that the movie was made) just to stand there and not play anything. The movie showed him eating Twix, and just staring off into space for the whole hour. And one of the violin players had just happened to choose that day not to play anything either, but to file her nails and flip through a magazine.
After the movie was over, those two musicians, as well as some others who had been publicly mortified, filed a civil suit against the conductor for defamation of character. At the trial, they testified before the judge: "Before the movie was shown, we all had good reputations as fine musicians. Now we are the laughingstocks of the musical world. Our careers might never recover from this. The conductor knew before he showed the movie to the world that it would result in our ruin, and yet he showed it anyway. Clearly, his intent was malicious, and we seek damages".
But then the conductor testified: "Your honor, I honestly had no malice toward these musicians. The procedure of making the film was quite random. We made scores of different films, and in many of them, these musicians played brilliantly. But the sound of the symphony as a whole on those days was unbearable to listen to, so those films had to be rejected. It was just by chance that the one day that sounded wonderful, they happened to have made fools of themselves by their own free will. They themselves chose to act that way that day. I didn't make them do anything".
The judge agreed and dismissed the case. He told the musicians: "I'm sorry, but you don't really have a legal leg to stand on. For you knew that the conductor was making a film of that day, and that the plan was to show it off to the world if it sounded good. It is your own fault that you chose to act the way you did that day" (cf. James 1:13-15).
Similar to this analogy, before God created the world, he could have reviewed an infinite number of different threads (as it were) of all the possible free-willed sequences of events which could occur in the world, based on all the possible choices each individual could make during his or her lifetime. For example, in one thread, right after God created Adam, Adam could have chosen first to walk around the south side of the Garden of Eden, while in another thread, Adam chose first to walk around the north side, and in another he chose first just to sit on the grass and look at the trees, and so on through all the different possibilities for his first choice, and then through all the different possibilities for all of his subsequent choices, and then through all the possible choices made by everyone else from the beginning of the world to the end of it. After reviewing the infinite number of threads of all the possible sequences of free-willed choices, God could have chosen to create, to bring into actual existence, that one thread which would give him the best opportunity to eternally show both his mercy and his holy wrath (Romans 9:22-23).
Also similar to the movie analogy is the scientific idea of the "block universe", meaning that time, from the viewpoint of physics in itself (i.e. outside of how humans happen to experience time) there is no arrow of time: The past, present, and future of all space in the universe exist as one block of a four-dimensional space-time. So the past still exists, and the future already exists. This is similar to how all the frames of a film, all its moments of time, exist at the same time in one reel of film, and yet we humans happen to experience a film only one frame at a time, and in one direction. Also, with regard to the "block universe", quantum-level experiments have shown that the future determines the past as much as the past determines the future. So from the viewpoint of Christians, this means that they can pray for God's will to be done in the past, just as they can pray for it to be done in the future. For example, if they remember a close call in their past when they just barely escaped having a car accident, they can presently pray that God would keep them from having that accident, and this could help them to avoid it. That is, they could have avoided it because years later they prayed to avoid it.
