Many suggestions have been put forth as to why the Midianites feared so greatly and began to kill one another. I think the bottom line is what is greatly implied in the text, God did what He said He would do. He not only fought for the Israelites, He put fear in their enemies and caused them to kill one another (7:19-23).
Why, even in the midst of this great deliverance by God, did other Israelites find it necessary to be a thorn in Gideon’s side; I am referring to the men of Ephraim, and the people of Succoth and Penuel (8:1-9)?
In his first test by the people Gideon was victorious. He said that neither he nor his son would rule over them, but that God would (8:23). But he immediately sinned even more greatly by requesting gold and making an ephod which the people then worshiped (8:24-27). The amount of gold was forty-two and a half pounds–over $867,710 today.
Perhaps we are being told more than first meets the eye in English at 8:31. Not only did Gideon have many children by many wives, but he had a son by a concubine, and the son was Abimelech . . . The name means “my father is king.” Did you also catch that two names were used for the same person in 8:29?
After Abimelech killed all his brothers but one, that one went to Mt. Gerizim and pronounced a blessing if they were right and a curse that would come about for their folly if they were sinning. Remember the significance of Mt. Gerizim is that it was where Moses was ordered by God to pronounce the blessing upon Israel along with six tribes, and Mt. Ebal was where with the remaining six tribes the curse was to be pronounced (Deuteronomy 11:29; 27:12-13) and which Joshua did (Joshua 8:33-35).
In this portion of Psalm 50 Asaph speaks words of God to sinners, “Who are you to talk about My laws? Everything you do is wrong. There is hope, but only if you were turn and obey.