Jeroboam said to himself, "[The way things are going] now, the kingdom might return to the house of David.
If these people regularly go to offer sacrifices in the Lord's temple in Jerusalem, the heart of these people will return to their lord, Rehoboam king of Judah. They will murder me and go back to the king of Judah."
So the king sought advice. Then he made two gold calves, and he said to the people, "Going to Jerusalem is too difficult for you. Israel, here is your God who brought you out of the land of Egypt."
References for 1 Kings 12:28
He set up one in Bethel, and put the other in Dan.
This led to sin; the people walked [in procession] before one of the calves all the way to Dan.
References for 1 Kings 12:30
Jeroboam also built shrines on the high places and set up priests from every class of people who were not Levites.
Jeroboam made a festival in the eighth month on the fifteenth day of the month, like the festival in Judah. He offered sacrifices on the altar; he made this offering in Bethel to sacrifice to the calves he had set up. He also stationed in Bethel the priests for the high places he had set up.
References for 1 Kings 12:32
He offered sacrifices on the altar he had set up in Bethel on the fifteenth day of the eighth month, the month he had decided on his own. He made a festival for the Israelites, offered sacrifices on the altar, and burned incense.
References for 1 Kings 12:33