Islamic theology (‘Aqeedah) is based on an ethical rather than speculative imperative. Many Qur’anic verses and hadiths show that Iman (faith) is obligatory and rewarded by paradise, and that kufr (unbelief) is wrong and punished by hell. We believe that Heaven and Hell exist and this is an intellectual possibility which doesn’t go against sound intellect.
I am not gonna delve into speculative theology much, I am gonna try to keep it simple. Suppose you have your final year exams coming up, the teacher tells you that if you don’t revise, you are gonna fail, but if you do revise then you will pass and go on to get that dream-job of yours or whatever. Now, for most of us, it’s the ‘fear of failure’ and not the ‘hope of success’, that makes us revise the hardest. Why? Human nature, that’s just how we are and how we think as human beings.
Now, if the Qur’an didn’t mention ‘hell’ (and only mentioned ‘heaven’), then the people would have questioned “Well, what about those who refuse to believe?” And if the Qur’an didn’t mention ‘heaven’ (and only mentioned ‘hell’), then the people would have questioned “What is there for the believers?” But if you analyse the Qur’an thoroughly, you’ll find that the words “paradise” and “hell” are each repeated 77 times; there is a perfect balance between ‘fear of failure’ (Hell) and ‘hope for success’ (Heaven), because our Creator knows what is best for us.
As for free-will, see it this way: “God creates the possibility of a human action with his divine predestination, but then the human follows through and “acquires” the act, making it theirs and taking responsibility for it using their human fate.” Simply put, God has knowledge of everything that will be, but humans have freedom of choice. For example, the teacher knows that the student is going to fail the exam, because he doesn’t study or attend any lectures. But the student is still given the chance to actually sit the exam without him being forced to do so. If he was to pull off an all-nighter the night before the exam and pass, that’d just show that the teacher is *not* all-Knowing, but God is.
I tried to keep it as simple as I could, but if you want me to discuss issues pertaining to theodicy and Euthyphro dilemma in-depth, then please leave a comment below.