In theory a prophet is supposed to serve the King by bringing the Word of God. But over history we see that the prophet when they do bring the Word of God to the king, it tends to conflict with what the king wants. This is especially the case here with Amos and the king and the kingdom of the North, Israel. Amos speaks about all of the terrible things that God has said he would do against Israel, and Amos pleading on behalf of the people that they would be spared.
God shows him the locusts that he has prepared to go against the land, Amos asks that he would not, and God does not. God shows him the fire he is about to bring down on the land and Amos asks that he would not, and God does not. God finally shows him a plumb line, which is used to define that which is level and uses it as an example of how he is going to destroy the city eventually.
It is after this last example that the upper echelon of Israel, the priest, the king, ask Amos to take his words and go South, to Judah, where he can prophesy terrible things against them. Amos' answer is unique. He says, I'm actually not even supposed to be a prophet. I just tend trees, sycamore trees, and God called me to come and speak. So, no, I'm good, I think I'll stay here.