Hosea 8:14
For Israel hath forgotten his Maker, and buildeth temples; and Judah hath multiplied fenced cities: but I will send a fire upon his cities, and it shall devour the palaces thereof. For Israel hath forgotten his Maker, and buildeth temples; and Judah hath multiplied fenced cities: but I will send a fire upon his cities, and it shall devour the palaces thereof.
Forgetting his Maker meant Israel turned to idolatry that grew from small beginnings. The forgetting began when Jeroboam set up two calves of gold as a first departure from established worship. That first departure led to grosser forms of idolatry until nearly all the inhabitants of the land gave themselves to nature worship and became deeply corrupted.