On the question of free will: even if you believe that unbreakable physical laws govern all physical processes, it is not impossible for free will to exist; improbable, perhaps, but not impossible. That's because, at a quantum level, physical laws are probabilistic, not deterministic. Free will could simply be power bestowed by God, if you will, on sentient entities (let's call them "souls"), to exercise control over quantum probabilities governing the atoms in human bodies. I'm not sure exactly how controlling the positions of electrons around atoms in your brain would translate into macroscopic phenomena, such as choosing to sin or not sin, but it's an interesting thought.
By the way, I've never actually studied quantum mechanics, so I could be way off. Ask a physicist, and they might tell you that physical laws are completely deterministic, without exception, in which case, the existence of free will would seem to require a violation of physical laws, a miracle, if you will. But if you're devoutly religious, then you probably believe in miracles anyway, so free will could still exist.