And he said unto Jether his firstborn, Up, and slay them. But the youth drew not his sword: for he feared, because he was yet a youth. He said unto Jether his first-born - By the ancient laws of war, prisoners taken in war might be either slain, sold, or kept for slaves. To put a captive enemy to death no executioner was required. Gideon slays Zebah and Zalmunna with his own hand. So Samuel is said to have hewn Agag in pieces, 1 Samuel 15:33. Benaiah slew Joab, 1 Kings 2:25. Saul orders his guards to slay the priests who had contributed to the escape of David, 1 Samuel 22:17; and David caused one of his attendants to slay the Amalekite who pretended to have slain Saul, 2 Samuel 1:15.
Related Commentaries of Judges 8:20
Judges 8:20
20 And he said unto Jether his firstborn, Up, and slay them. But the youth drew not his sword: for he feared, because he was yet a youth.