Background:
Jeroboam, the first king of the northern kingdom of Israel, reigned during a tumultuous period marked by idolatry and rebellion against the Davidic line. Abijah, the son of Rehoboam and grandson of Solomon, ruled over the southern kingdom of Judah. The conflict between Jeroboam and Abijah is a significant event that underscores the divine favor upon the house of David and the consequences of turning away from the Lord.

Biblical Account:
The account of Jeroboam's defeat and Abijah's strengthening is primarily found in 2 Chronicles 13. Abijah ascended to the throne of Judah and faced a formidable adversary in Jeroboam, who had led Israel into idolatry and away from the worship of Yahweh. The two kings met in battle at Mount Zemaraim in the hill country of Ephraim.

Abijah's Speech:
Before the battle, Abijah stood on Mount Zemaraim and addressed Jeroboam and all Israel. He reminded them of the covenant God made with David, emphasizing the legitimacy of his rule over Judah. Abijah declared, "Do you not know that the LORD, the God of Israel, has given the kingship of Israel to David and his descendants forever by a covenant of salt?" (2 Chronicles 13:5). He condemned Jeroboam's rebellion and the establishment of golden calves as objects of worship, contrasting it with Judah's continued adherence to the true worship of Yahweh.

The Battle:
Despite being outnumbered, with Jeroboam's forces numbering 800,000 and Abijah's only 400,000, Abijah's faith in the Lord was unwavering. Jeroboam attempted to ambush Abijah's troops, but Abijah cried out to the Lord, and the priests blew the trumpets. The men of Judah raised a battle cry, and God delivered Jeroboam and all Israel into their hands. "So the Israelites fled before Judah, and God delivered them into their hands" (2 Chronicles 13:16).

Divine Intervention:
The victory was attributed to divine intervention, as the chronicler notes that Judah prevailed because they relied on the Lord, the God of their ancestors. The defeat was devastating for Jeroboam, who lost 500,000 of his men, a significant portion of his army. This event marked a turning point, as Jeroboam never regained his strength during Abijah's reign.

Abijah's Strengthening:
Following the victory, Abijah grew in strength. He took several cities from Jeroboam, including Bethel, Jeshanah, and Ephron, along with their surrounding villages. The Lord's favor was evident in Abijah's reign, as he continued to fortify his kingdom and maintain the worship of Yahweh in Jerusalem.

Theological Significance:
The defeat of Jeroboam and the strengthening of Abijah serve as a testament to God's faithfulness to His covenant with David. It highlights the importance of true worship and reliance on the Lord. Abijah's victory is a reminder of the divine protection and blessing that accompany obedience to God's commands, contrasting sharply with the consequences of idolatry and rebellion as exemplified by Jeroboam's downfall.