How do I know the things I know?

[Darkstar]

This is like saying if free-will was observable, then no one would disbelieve in free-will.

Yet most of humanity believes free-will is observable through our own experience of it.

Yet there exists people whom disbelieve in free-will.

Do you conclude on this basis free-will is not observable?

You actually bring up an interesting point. I take 'reveal' not to simply mean doing something that is observable, but in fact something that should be attributed to him. If god wanted to 'reveal' himself, he would not do something that would be ambiguous. Free will has yet to be truly defined; how much control does one need to be 'free'? We cannot even begin to guess, as our mental processes are so complex that we can't tell.

"The lord doesn't work in mysterious ways, but in ways that are indistinguishable from his nonexistence."

Thanks again to teaearlgreyhot's sig
At this point, free will is indistinguishable from lack of it (we at least have the illusion of it), but if god truly were to 'reveal' himself, he would not act in a way indistinguishable from a totally normal event.