Why did Amatziyah send to Yaravam?
Radak: Amos prophesized these Nevu'os in Beis Kel. Amatziyah, the priest of the idolatry there, heard them and sent to Yaravam that Amos conspired against him. Yaravam was not in Beis Kel at the time; Amatziyah sent to where he was at the time 'Amos prophesizes evil for you.' Amos was under Yaravam's sovereignty ? he was from Bnei Asher. He is Chayav Misah for saying that the king will die by the sword (11) ? he rebels against you! Malbim ? via saying so, he arouses a conspiracy against the king. People will stand to kill him, for the Navi said so in the name of Hashem, just like Yehu conspired and killed his king based on a Navi's Nevu'ah.
Malbim: He was upset that Amos prophesized about the Bamos and Mikdashim.
Was he a proper Kohen?
Rashi: No ? he was a priest of his idolatry.
Can the land not contain all his words?
Radak: The people of land cannot bear all his words ? he speaks evil about Yisrael.
Malbim: It is as if the land cannot bear his Nevu'ah ? therefore, you need not fear to kill him lest the nation wage his quarrel. He prophesized punishments also for the nation, to the point that they will agree to kill him.
