It was Gideon's place to act the part of the "avenger of blood" Numbers 35:12; Deuteronomy 19:6. The fierce manners of the age break out in the slaying of the captives (compare 1 Samuel 15:32-33), and in Gideon's attempt to initiate his youthful son Jether in the stern work of slaying his country's enemies.

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.

And he said unto Jether, his firstborn, up, and slay them,.... Being the near kinsman of his father's brethren, whom these kings had slain, was a proper person to avenge their blood on them; and the rather Gideon might order him to do it, for the greater mortification of the kings, to die by the hand of a youth; and for the honour of his son, to be the slayer of two kings, and to inure him to draw his sword against the enemies of Israel, and embolden him to do such exploits:

but the youth drew not his sword, for he feared, because he was yet a youth; his not drawing is sword was not out of disobedience to his father, but through fear of the kings; not of their doing him any harm, being bound; but there was perhaps a ferocity, as well as majesty in their countenances, which made the young man timorous and fearful.

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.

8:20 Up, and slay - That he might animate him to the use of arms for his God and country, and that he might have a share in the honour of the victory.

20. he said unto Jether his first-born, Up, and slay them-The nearest of kin was the blood-avenger; but a magistrate might order any one to do the work of the executioner; and the person selected was always of a rank equal or proportioned to that of the party doomed to suffer (1Ki 2:29). Gideon intended, then, by the order to Jether, to put an honor on his son, by employing him to slay two enemies of his country; and on the youth declining, he performed the bloody deed himself.

8:18-21 The kings of Midian must be reckoned with. As they confessed themselves guilty of murder, Gideon acted as the avenger of blood, being the next of kin to the persons slain. Little did they think to have heard of this so long after; but murder seldom goes unpunished in this life. Sins long forgotten by man, must be accounted for to God. What poor consolation in death from the hope of suffering less pain, and of dying with less disgrace than some others! yet many are more anxious on these accounts, than concerning the future judgment, and what will follow.