Causality

I will define the concepts better as I do not understand it and maybe that is where my failure lies.
Cause – is the cause of a thing, meaning that everything that exists or happens has a cause that forces it. The cause of course forces the whole thing and forces it exactly in the way it is or happened.
Free choice – there is a possibility of breaking out of the circle of circumstantiality, that is, breaking out of the necessity of causing in certain situations.
Purpose – is the motivation from which the chain of reasons is created, i.e. a person who goes to buy food, the purpose is his desire to eat and it creates a chain of going to the store and buying food and paying and the act of eating, the purpose creates the chain of reasons, but of course the purpose also has a reason, i.e. there is a reason why a person wants to eat.
The question is, it is clear that there is a factor that acts on a person, but the factor still does not force the result. If the argument for free choice is that there is an additional component in a person, and we define it for the purpose of the discussion as the component of the soul that allows a person to create a factor by choice, that is, to create a factor that does not have a factor that forces it, I can understand it and of course it cannot be proven, but I did not understand what the concept of purpose helps with. After all, purpose is a person’s final will and it also stems from a reason. If so, purpose is also a circumstantial product, then what have we gained and what is purpose without a reason? In short, to say purpose without a reason is to say a reason without a reason, because the concept of purpose can also be applied to the question of whether it has a reason or is it random.
In short, as you can see, I’m a little confused and can’t seem to fully understand the point.