Free means self-caused - only that which is self-caused, and that which is capable of self-causation, can be free.
Free does not mean un-influenced. That which causes is often subject to external influence but free means that behaviour cannot wholly be explained by influences.
Ultimately, freedom cannot be explained - nothing self-caused can be explained.
Thus, freedom is irreducible. We cannot know what goes-on, or how freedom arises.
There is no 'natural' (analytic, rational, scientific) explanation for what leads-to freedom (or else it would not be free). Freedom stands outside cause and effect.
Indeed, freedom is divine in nature.
We can perceive only the result of freedom; and all we can do is just take it, or leave it.
We may, or may not, be aware of that which is free - but it emerges complete and ready; so all that can be done-about freedom is to accept or reject it (whether unconsciously or deliberately).
Therefore, it is crucial to know whether that which is innately free is good, or evil.
This is the question of original sin.
Is that essential-self which is free basically evil/ sinful in nature; or is it good/ of God?
One or the other must be assumed.