There is a story that America, before dropping the atomic bombs in World War II, first dropped leaflets or pamphlets on Hiroshima and Nagasaki that warned of the bombing. I cannot vouchsafe the truth of the story, but it is quite the parallel to what God had to say through Amos.
The nothing in this verse is either a very poor choice of words or a limited version of itself. In English, we often say that someone does nothing without doing some other thing. We comment that a person does nothing before washing their hands which is patently absurd because something had to have happened before that hand washing. What we actually mean is that the individual performs none of a certain kind of action without first washing their hands — a fact about which we are all glad to hear in the case of folks who cook for us. Likewise, I think, this verse is not saying that God does absolutely nothing without revealing it to the prophets — there is plenty that He does that we probably would not understand if He took the rest of eternity to explain it to us — but rather that God does not do a certain set of things without revealing them to the prophets. In context, we could reasonably conclude that the subset of actions pertain to judgment and discipline. And scripture bears out that God did not discipline without first sending a notice to the Israelites through the prophets.
Which brings me back around to that World War II illustration. The danger in the United States dropping warnings on the cities to be bombed is that America shows her hand. The cards are dealt open and everyone who has a stake in what happens knows what is coming. So many things could have happened; so many things could have been done to interrupt the plan to bomb those cities. Likewise, God has a tendency to reveal His big plans. Throughout the OT (Old Testament), God drops steadily more detailed information about how He plans to redeem humanity. It begins with a promise to Eve that the seed of the woman will crush the head of the seed of the serpent. It becomes a promise to Abram, later renamed Abraham, that narrows the scope to a bloodline. On down through the ages, God reveals a little at a time of His grand design, as if daring His enemy to stop Him; as if warning that the end of the war is approaching. And that is precisely what is coming.
Sun Tzu once wrote that the victorious strategist only seeks battle after the victory has been won. God, I suspect, did not utter the words “Let there be light.” until He had already planned His victory over sin and death; planned His redemption of humanity. And built into His plan was revealing that plan to both friend (Jesus says that He calls us friend if we do as He instructs — John 15:14-15) and foe. He reveals His plans for discipline and judgment and redemption. If it is a big deal, then God has said something about it. If God has stayed mum, then it is not as big a deal as I am making it out to be.
And that is the application for me this morning. If it is a big deal; if it is important, then God will have said something on the matter; will have revealed His heart through the prophets. If God has said nothing on the subject, not even obliquely hinting at it, then it is likely not the catastrophic thing I seem to think it is. In my experience, He is happy to provide me input on the small stuff, but that input is tailored to me, not necessarily generally applicable. God reveals the necessary and important; the big stuff.