Bible Notes Online - 2-Chronicles 13 - ESV
Commentary

v1-3: During the reign of Abijah, Rehoboam's son, there was a larger battle than previously.

v4-12: Abijah's declaration of faithfulness to God.

Abijah referred to the history of Judah and Israel, and God's choice of David (v8), and of Levi (v9). Israel had rebelled against the Lord in neglecting those chosen by Him. In particular, Jeroboam rebelled against Solomon, which led to the rebellion against Rehoboam, when he was young and indecisive. They took advantage of Rehoboam's youth. This interpretation of the history is generous to Rehoboam.

Israel fell into idolatry (v8), and appointed priests from all classes of people (v9).

In contrast, according to Abijah, Judah remained faithful (v10-11), and therefore God would be faithful to His faithful people, and protect them against the faithless aggressor.

v13-15: Jeroboam pretended to listen to Abijah's message, but showed no sign of repentance. In the meantime, he sent his troops to ambush Judah, depending on military strategy and human wisdom.

Judah cried out to God in prayer, and God delivered them, although Judah had not been particularly faithful. Here is God's grace towards His own people.

v16-18: Israel suffered a serious defeat. God gave Judah victory because they relied on Him.

v19-20: Abijah took the opportunity to capture some southern Israelite towns. He thus weakened Jeroboam.

v21-22: Abijah followed his forefathers' examples in having many wives.