I suspect this question makes a bit more sense if we take it out of its context speaking about the Bible, and just analyze the basic question… for instance:
When God made the statement to Moses from the burning Bush, “I Am the God of Abraham, Isaac, and Jacob,” i easily grasp that such a statement, if actually made from the God of the Universe is indeed “self-attesting”… in the sense that, what higher authority could we use to “test” God’s own words. We know that the voice that was speaking to him was indeed the God of Abraham et al… because why? Because the eternal God just said so. what else do we need?
That said, there is another important angle… it seems reasonable for Moses to perhaps considered the logical alternatives: had he eaten some undercooked lamb the night before, and was hallucinating? had he fallen asleep and had a waking dream? was some fool Egyptian ventriloquist playing a trick on him? ones, presumably having excluded these alternatives, apparently recognized the voice as indeed being God’s own.
So I suspect there is indeed a place (i think this is what Grudem is getting at) where we use our reason, evidence, and the like in order to “authenticate” that the message really is from God (by excluding other alternatives and other such reasoned methods)…but, once we have recognized the message’s source as God himself, then we recognize that everything it communicates is indeed true… including any “self-atteststion”.
I compare it to what was seen in the submarine movie “Crimson Tide”… as the movie portrays it, when a radio message is received that claims to be from the President/Pentagon or whatever, they don’t just blindly and immediately do whatever it said to do (launch the nuclear weapons at such and such target) , as there is the possibility that the message could be a forgery. the movie portrayed a method by which the message was “authenticated” and thus confirmed that it really came from The president/pentagon… but once said message was so authenticated, then the submarine officers were duty-bound to do whatever it said, whether or not they understood it, agreed with it, or the like.
this didn’t mean that they were claiming that they had greater authority than the president, rather, they reasonably authenticated the message and confirmed it as actually coming from the president… once they did that, however, they realized that they had to submit and obey whatever the message said, as it was recognized as being from the president.
I would humbly posit that there are indeed reasonable steps by which we similarly “authenticate” Scripture to be God’s words, but once we do, then we as believers are duty bound to believe and obey whatever God has indeed communicated… - including any so-called “self-attestation”
thoughts?