Theodoret of Cyrus
The descendants of Ephraim prepared for battle against Jephthah, feeling bitter that they had not participated in the triumph over the Ammonites. When their efforts proved fruitless, they eventually retreated.
Then calling to him all the men of Galaad, he fought against Ephraim: and the men of Galaad defeated Ephraim, because he had said: Galaad is a fugitive of Ephraim, and dwelleth in the midst of Ephraim and Manasses.
וַיִּקְבֹּ֤ץ יִפְתָּח֙ אֶת־כָּל־אַנְשֵׁ֣י גִלְעָ֔ד וַיִּלָּ֖חֶם אֶת־אֶפְרָ֑יִם וַיַּכּוּ֩ אַנְשֵׁ֨י גִלְעָ֜ד אֶת־אֶפְרַ֗יִם כִּ֤י אָמְרוּ֙ פְּלִיטֵ֤י אֶפְרַ֙יִם֙ אַתֶּ֔ם גִּלְעָ֕ד בְּת֥וֹךְ אֶפְרַ֖יִם בְּת֥וֹךְ מְנַשֶּֽׁה׃
2 Church Fathers comment on this verse
The descendants of Ephraim prepared for battle against Jephthah, feeling bitter that they had not participated in the triumph over the Ammonites. When their efforts proved fruitless, they eventually retreated.
The insurgents were relentless, referring to the people of Gilead as outcasts who had departed from the genuine lineage of Joseph. This led to a confrontation in which Jephthah triumphed and dispersed them.
Passages read together with this verse.