"'Sound the trumpet in Gibeah, the horn in Ramah. Raise the battle cry in Beth Aven; lead on, O Benjamin.'" NIV translation
Beth Aven which means "house of wickedness" was another name for the city of Bethel which means "house of God". God is sending a warning to the people that they have gone from being a house of God to a house of wickedness.
"'Ephraim will be laid waste on the day of reckoning. Among the tribes of Israel I proclaim what is certain.'" NIV translation
The "day of reckoning" also known as the "day of the Lord" is the time of judgment. Here, we see that, because of their turning away from God, they will be judged and God has made up His mind. God is the same today and we, too, will be judged if we trust in anyone or anything except Jesus Christ.
"'Judah's leaders are like those who move boundary stones. I will pour out my wrath on them like a flood of water.'" NIV translation
Not only had Israel (the northern kingdom) turned their back on God but Judah had done the same. Today, we have gps to tell us the exact location of anything but, in the days of Hosea, property boundaries were marked by a rock or rocks. Someone who moved the boundary stones would be considered a liar and a thief. That is what God is saying that the leaders of Judah had become. When the leaders of a nation become corrupt, the people usually follow. God will punish the corrupt even Judah (His religious leaders).
"'Ephraim is oppressed, trampled in judgment, intent on pursuing idols. I am like a moth to Ephraim, like rot to the people of Judah.'" NIV translation
Because they turned away from God, the people are judged. To them, obeying God had become a bother and so they went after idols. We may think that it is crazy to turn away from God and chase idols but we have to ask ourselves if we are not doing the same thing. Today, many of the idols are in the form of material things such as a fancy home, car, or retirement account and many put all of their efforts into those things.