The lion has roared; who will not fear? The Lord GOD has spoken; who can but prophesy?”
It now follows, The lion roars who would not fear? The Lord Jehovah speaks, who would not prophesy? In this verse the Prophet reproved the Israelites for their usual contentions with the Prophets when their sins were sharply reprehended. Thus indeed are men wont to do; they consider not that Prophets are sent from above, and that there is a charge committed to them.
The scope of these verses is to convince the people of Israel that God had a controversy with them. That which the prophet has to say to them is to let them know that the Lord has something to say against them, Amo 3:1.
Commenting on Amos 3:1-8
Publish in the palaces at Ashdod, and in the palaces in the land of Egypt,.... This is spoken to the prophets, to publish and declare in all the courts of the Philistines and Egyptians, and among all the princes and great men therein, the sins of the people of Israel, and the punishment God threatened them with; and let them, even these very Heathens, judge...