It’s usually those not involved in the battle who whine the most and loudest about the war. Israel’s victory over Ammon was more difficult for the tribe of Ephraim to accept than 18 years of living in defeat (Judg 10:8). As with Gideon, Jephthah’s most trying enemy was his own people. The same was true of Jesus, who came unto His own only to be rejected by them (John 1:11).
Leadership is a gift from God, but never a tool for self-approval, self-advancement, or self-fulfillment. The man God used, Jephthah, was without a father, rejected by his brothers, and had no son. His life was sandwiched between a prostitute mother and his virgin daughter. Chosen to represent all of Israel, he ended up a strict partisan, the writer of Judges pointing out two dozen times his tribal connection (Judges 10:17-12:7).

I. Contention (Judg 12:1-3). The tribe of Ephraim crossed eastward over the Jordan River to confront Jephthah, angry he didn’t include them in his victory and threatening to burn down his house. Ephraim decades earlier accused Gideon of the same (Judg 8:1). About 120 years later, the kingdom of David and Solomon would be split, and it was Ephraim at the center of the rebellion (1 Kin 11:26; 12:1-25). Ephraim eventually became a synonym for the godless northern kingdom for 200 years.

When there is success, there will be no end of those who want rewarded, even if they didn’t participate in the victory. In failure, these are the same who will be first to lay blame.
Division is the ugly child of the marriage of pride and jealousy. Pride and jealousy can’t admit to being wrong, desire honor and recognition, and are easily offended by small things. Christians must instead be humble (Phil 2:1-8).

II. Combat (Judg 12:4-9). Jephthah once again tried to negotiate as he did with the leaders of Gilead (Judg 11:4-11), the king of Ammon (Judg 11:12-27), and God (Judg 11:30-40). Though he’d called Ephraim to battle, they’d rejected him. God delivered the enemy into Israel’s hand without Ephraim’s help. Jephthah wasn’t Ephraim’s enemy. Make sure you have the right enemy before you pick a fight (Eph 6:12).
Deliverance is a two-part work; from one thing unto another. For example, God has called believers out of darkness into His marvelous light (1 Pet 2:9), out of sin into righteousness (1 Pet 2:24), and from idolatry into Godly worship (1 Thess 1:9).
Ephraim’s leaders hurled insults at Jephthah and his men, calling them fugitives or literally escapees or wimps, claiming the weakest in Ephraim was stronger than Jephthah, a fugitive from his own family. The nation was divided.
Civil war broke out between Ephraim and Jephthah. Jephthah’s men took the towns along the Jordan River, effectively keeping the Ephraimites from returning home. The password to cross the Jordan was shibboleth, meaning a flowing stream, but the Ephraimites couldn’t make the sh sound. Then Jephthah’s men slaughtered 42,000 Ephraimites. God’s victory over Ammon was overshadowed by the sins of Israel, which became more evil with each generation.

III. Christ. Jephthah judged Israel 7 years, but God didn’t give the nation rest (Judg 3:11, 30; 5:31). Jephthah started well, but finished poorly, doing what was right in his own eyes. He overcame so much early on, only to be overcome by his own ego. His sin didn’t cause him to lose his salvation (Heb 11:32), but he certainly lost his testimony with you and me!
This failed judge points us to the perfect Jesus. Jesus is a Deliverer for all peoples, tribes and tongues (Ps 86:9; Mt 28:18-20; Jn 1:11-13; Acts 1:8; Rom 1:16; Rev 5:9-10; 7:9; 14:6-7). He always kept His eyes on the Father (Lk 2:49; Jn 4:34; 5:18-20; 6:38; 8:28-29; 12:49; 17:4; 19:30; Phil 2:8), finishing well, affirmed by His resurrection (Rom 1:1-4) and ascension (Acts 7:55-56; Rom 8:34; Col 3:1).