The grace of God means something like: Here is your life. You might never have been, but you are because the party wouldn't have been complete without you.
It is as impossible for man to demonstrate the existence of God as it would be for even Sherlock Holmes to demonstrate the existence of Arthur Conan Doyle.
If enough people openly engage in conduct once considered reprehensible, we rewrite the rule book and assume that God, as a good democrat, will go along.
Unfortunately, in today's world we have to be reminded that the power of an oath derives from the fact that in it we ask God to bear witness to the promises we make with the implicit expectation that He will hold us accountable for the manner in which we honor them.
The parents have a right to say that no teacher paid by their money shall rob their children of faith in God and send them back to their homes skeptical, or infidels, or agnostics, or atheists.