Why should they blow a Shofar?
Rashi: They should be careful to guard from the sword of troops that will come against them.
Rashi citing Targum Yonasan: This heralds that the sword will come due to the sin of making Sha'ul, who was in Giv'ah, king. They did not heed the voice of Shmuel, who was from Ramah. Their kings caused them to veer from me, e.g. Yaravam and his colleagues.
Radak: Just like they blow a Shofar to warn the nation and to gather to the city 1 .
Radak citing Targum Yonasan: Nevi'im, raise your voices like a Shofar?
Malbim: When Hoshe'a began to prophesize, Yehudah was submissive to Efrayim, from when Yaravam ben Yo'ash conquered Amatziyah. Also in the days of Achaz, Pekach ben Remalyahu conquered Bnei Yehudah.
Radak adds 'and the Tzon.' I do not understand this. (PF)
Why should they blow Teru'ah in Beis Aven?
Radak: The previous places are of Binyamin. Beis Aven was of Bnei Yosef, in Efrayim, close to Binyamin; Binyamin was between Yehudah and Yosef.
Malbim: Also Beis Aven was in Binyamin. It says about Binyamin's border "v'Hayu Totze'osav Midbarah Beis Aven" (Yehoshua 18:12). Refer to 5:8:3:3.
Why does it say "Acharecha Binyamin"?
Rashi: It is because Ichartem (you delayed) and went back from ascending for the Regel to the Beis ha'Mikdash, which is in Binyamin's portion.
Radak: After you, the enemy will go to Binyamin, for it already conquered Eretz Efrayim.
Malbim: This warns the people not to go after Efrayim, rather, after Binyamin, which is connected to Malchus Yehudah, and to separate from Malchus Efrayim.
