I've heard the expression, "All truth is God's truth," before. I never stopped to consider it. I think there's no doubt that people who've made that statement must often have fundamentally different perspectives. I don't think that the statement necessarily denigrates God's Word, even though some probably intentionally use it to do just that. I'm told that this notion is found in the original preface to the King James Bible, although I can't be sure of that. I don't have an old one handy.

I don't think I have a problem with the statement as such. If I were to use it, it would be to say that although I look to the Bible as the ultimate authority and final in all matters of truth and doctrine, it isn't the only way we receive revelation from God.

I believe in sola scriptura as opposed to nuda scriptura, but there is "general revelation." God has manifested Himself to us through history and He does so in nature and to our conscience, and in these things His truth is seen as well. One probably shouldn't interpret such things without holding them up to the light of Scripture, but they are a part of our physical and spiritual reality.

If I just ignore a statement like, "All truth is God's truth," I might be ignoring a particular way that God wants to use make me to learn about Him. So if I heard someone else use it, I'd probably have to have them define what they meant by it so that I could converse intelligently with that person. Little statements like that can cause real confusion if they aren't explored.

Personally, I would probably favor the statement, "All truth of any lasting value comes from God," but I suppose a skilled philosopher might be able to get nit picky with that too. :)