How did Hashem afflict and strengthen their arms?
Rashi: I strengthened via My Nevi'im, that people should listen to their reprimand.
Radak: When they had good, and they were strong against their enemies. Yisarti is like "Musar Melachim", "u'Moseros Arod" (Iyov 12:18, 39:5), i.e. tying. Tying strengthens a matter.
Radak citing Targum Yonasan: I brought afflictions on them to strengthen their hands.
Malbim: I thought that via afflicting the Ben Sorer u'Moreh, they will repent and I will strengthen them ? "Aisirem? la'Adasam; ? v'Anochi Efdem" (12-13).
What evil do they think about Hashem?
Radak: They think that the good and bad are not from Him ? they are chance.
Radak citing Targum Yonasan: They intended to do more evil.
Malbim: They think that Hashem does evil, and does not intend for good.
