Judges 13:1 - Wesley's Explanatory Notes

Did evil — That is, fell into idolatry, not after the death of Abdon the last judge, but in the days of the former judges. Forty years — To be computed, not from Abdon's death, but before that time. And it is probable that great slaughter of the Ephraimites made by Jephthah, greatly encouraged the Philistines to rise against Israel, when one of their chief bulwarks was so much weakened; and therefore began to domineer over them not long after Jephthah's death. These were a very inconsiderable people. They had but five cities of any note. And yet when God used them as the staff in his hand, they were very oppressive and vexatious.