Malbim: He said the idolatry was the cause of the afflictions. They said oppositely. In the days of Achaz and Menasheh, they served idolatry constantly, but the evil came only in the days of Tzidkiyah, when most people served Hashem and heeded the Nevi'im! They said that this shows oppositely, that idolatry helps and protects them, and when they slackened and did not offer to Meleches ha'Shamayim, the evil came on them! The Haktarah had a Segulah to bring down influence, from the stars and constellations, of dew and rain of Brachah. They thought that via ceasing to offer, they lacked everything.