Yerovam has become king in the North. But he needs a new religious center. If the prople keep celebrating their holidays at the Temple in Jerusalem, he will lose legitimacy.
Yerovam builds two new Temples in Dan and Bethel setting up a golden calf (!) in each shrine. But, the Tanakh tells us that this was a grave error.
Chapter 13 reveals the people's confusion. Is Yerovam legitimate or illegitimate?