I strongly recommend reading the post on the problem of evil first, as it is a closely related question in dealing with why God allows certain things that may seem odd to us. This post will assume you are already familiar with it.
In the Bible, we see that two principles guide the events of the earth. First, the principle of divine sovereignty means that God oversees the events of the universe. He is all-powerful (Isaiah 45:6-7, for example), and He possesses a plan for the world (Isaiah 14:26-27). Secondly, humans are afforded free will, the principle of being able to make their own choices regardless of whether it is right or not (within the boundaries of natural law – we cannot fly, become invisible, etc.). One argument against Christianity focuses on the apparent contradiction between the two. In other words, if God’s will reigns supreme, then our choices aren’t really OURS, are they? And if free will reigns supreme, then God’s total sovereignty is likewise dealt a blow.
The contradiction, however, relies on an extra assumption, and you may have already noticed it – free will and divine sovereignty would need to be proven as advancing separate goals entirely. For the argument against Christianity to work, one would need to show that the existence of free will runs counter to God’s plan.
From the very beginning of the Bible, we see that God made us in His image, including the power to think and speak. It was free will that allowed for the possibility of Adam and Eve’s original sin, as well as all our sins afterwards. As this site’s post on evil has shown, the mere existence of evil does not disprove a Christian God (and even helps to prove God instead). For one to properly show love, there must be an opportunity for them to show the absence of love. Otherwise, as C.S. Lewis puts it, they are reduced to a mere machine, operating at the whim of someone above them. We know that this is not what God wants.
One commonly accepted solution to this problem among Christians is the concept of God controlling the framework of history through complete knowledge of events. There is a broad framework of events set by God, and free will, which fits inside of that framework, is allowed to operate normally. As God is all-powerful, He controls the ultimate destiny of the world, and knows the consequences, both possible and actual, of allowing the world to take a certain course (see Molinism in the further reading section for a more specific idea of how this could work). He sets that course, and by and large man is able to make their own decisions, yet those decisions do not break God’s plan.
Here is one example of having both concepts co-exist: Being an amazing cook, you give a person you know well two possible meals to choose from. But, you also know that they like one of those meals, while disliking the other. This is akin to the knowledge God possesses. The person still has a choice, but at the same time the cook knows there’s a predisposition to one of those meals.
God knows us better than we know ourselves (Hebrews 4:13), yet He also allows us to occasionally stumble and rebel as He knows even the best of us will. He could have easily judged us right there and then, but instead He gave us Jesus. The heavy price paid by Jesus’s sacrifice is truly the greatest reward we could ever ask for – the opportunity to get back up after a fall!
Another point that I want to mention: During my research for this post I stumbled upon a counter-argument for free will and God’s will coexisting saying that since several people in the Bible were at the receiving end of God’s judgment, their free will was denied. One quote I heard sums the answer up nicely: you have the power to choose your actions, but you do not have the power to change the CONSEQUENCES of those actions. For example, Lot and his family were fleeing the destruction of Sodom and Gomorrah in Genesis 19 (this was one of the examples used for the counter-argument). They were instructed not to look back while they were fleeing, but Lot’s wife did, and she became a pillar of salt. It was her free will to disobey God’s direct order, but the consequences naturally followed.
‘A Beginner’s Guide to Free Will‘ by DesiringGod
Audio of William Lane Craig on Molinism, one specific theory as to what God’s providence with respect to free will looks like. Getting into the specifics of Molinism is beyond the scope of this site. In general, Craig’s discussions are very technical.
Craig also wrote a book called The Only Wise God: The Compatibility of Divine Foreknowledge and Human Freedom