Abijah reigned over Judah in the south from 913-911 B.C., 2 Chronicles 1:22-14 / 1 Kings 15:1-8. Some translations have his name as Abijam.
He just like Rehoboam, continued to lead God’s people in idolatry and it’s clear that he simply wanted to please the people around him because his heart wasn’t devoted to God.
For David’s sake, 1 Samuel 13:14 / Acts 13:22, Abijah’s son, Asa was given the right to rule as king in Jerusalem by God. God did this in order that the seed promise of the Messiah would be fulfilled, Genesis 12:3.
Once again we read about war, this war was between the northern kingdom and the southern kingdom, this is brother against brother.
The covenant of salt was a continuous covenant between God and Israel, Leviticus 2:13. As far as Abijah was concerned, he thought the northern tribes no longer honour this covenant, because of the division of Israel. He basically accused them of rejecting the covenant and hiring priests who weren’t Levites.
Jeroboam sets up an ambush to go around behind them, however, when the battle lines unexpectedly changed, knew that a surprise attack from an army twice as large as them left them in a very dangerous place.
The only thing they could do was cry out to God. They cried out to God and God struck the army of Israel and Judah won, simply because they relied on God.
Since Jeroboam had taken the northern tribes further away from God and since he became king over the northern tribes, God fought for Abijah. This resulted in the death of 500,000 Israelites and the defeat was so great that the north under the rule of Jeroboam was never able to regain military strength,1 Kings 14:20 / 1 Kings 15:9.
Barnes, in his commentary, says the following.
‘It has been proposed to change the numbers, here and in 2 Chronicles 13:17, into 40,000, 80,000, and 50,000 respectively, partly because these smaller numbers are found in many early editions of the Vulgate, but mainly because the larger ones are thought to be incredible. The numbers accord well, however, with the census of the people taken in the reign of David 1 Chronicles 21:5, joined to the fact which the writer has related 2 Chronicles 11:13-17, of a considerable subsequent emigration from the northern kingdom into the southern one. The total adult male population at the time of the census was 1,570, 000. The total of the fighting men now is 1,200,000. This would allow for the aged and infirm 370, 000, or nearly a fourth of the whole. And in 2 Chronicles 13:17, our author may be understood to mean that this was the entire Israelite loss in the course of the war, which probably continued through the whole reign of Abijah.’
Jeroboam rebelled against his lord, that is, the house of David because God had given him the right to reign over the northern ten tribes. If anyone came with a bull and seven rams, he could be a priest, Exodus 29:1 / Leviticus 8:2. In other words, Jeroboam was selling the office of a priest.
Abijah speaks against the northern tribes and tells them they will not succeed because they have moved too far away from God’s will. Although God had given the ten northern tribes to Jeroboam, Jeroboam took them into idol worship.
Notice God struck Jeroboam down and killed him, in other words, God used the army of Judah to judge the northern tribes because they followed Jeroboam.
Barnes, in his commentary, says the following.
‘Jeroboam’s death was a judgment upon him for his sins. Chronologically speaking, his death is here out of place, for he outlived Abijah at least two years, compared to the marginal reference and 1 Kings 15:9, but the writer, not intending to recur to his history, is naturally led to carry it on to its termination.’
Abijah grew in strength, 1 Kings 15:3, and here again, we find a reference to the annotations of the prophet Iddo, which have a record of Abijah’s reign and everything he said and did, 1 Kings 15:7.
"So Paul stayed for a year and a half, teaching them the word of God."