The temptation against which the teacher seeks to guard his disciple is that of joining a band of highway robbers. The “vain men” who gathered around Jephthah Judges 11:3, the lawless or discontented who came to David in Adullam 1 Samuel 22:2, the bands of robbers who infested every part of the country in the period of the New Testament, and against whom every Roman governor had to wage incessant war, show how deeply rooted the evil was in Palestine. Compare the Psalms 10:7, note; Psalms 10:10 note.
Without cause - Better, in vain; most modern commentators join the words with “innocent,” and interpret them after Job 1:9. The evil-doers deride their victims as being righteous “in vain.” They get nothing by it. It does them no good.