“At that time 42,000 of the Ephraimites fell” (v6). Sadly, when the Israelites were not being attacked by outside enemies, they were attacking each other in the time of the judges. Without a king or a strong commitment to worshiping God and following the Law together, the tribes became competitive and distrustful. They had different leaders and different ways of talking (Shibboleth vs Sibboleth), and alliances between tribes were uncertain and fragile (v3). Rather than stand together, they tore each other apart.
“Are you an Ephraimite?” (v5). Human nature divides us into competing tribes. True unity is found in being “in Christ,” in whom there is no Jew or Greek, slave or free, male or female (Galatians 3:28).