Judges 8:20 is a pivotal verse in the story of Gideon's pursuit of the Midianite kings Zebah and Zalmunna. Here's a breakdown of its meaning:

Context: Gideon, having defeated a large Midianite army, is chasing the remaining kings. He captures them and is now enacting vengeance for the wrongs they committed, particularly the killing of his brothers.
"He said to Jether his firstborn, 'Get up, and kill them!'": Gideon orders his eldest son, Jether, to execute the captured Midianite kings. This would have been a highly symbolic act.

Why his son? Publicly executing the kings by his own son would be a powerful statement of Gideon's authority and the complete defeat of the Midianites. It would also be a way of avenging his murdered brothers directly through his lineage.
Why execute them? Gideon is acting as a judge and avenger. The Midianite kings were responsible for the deaths of Gideon's brothers and were a threat to Israel's peace. In the context of the time, such actions were seen as justified and necessary.
"But the youth didn’t draw his sword; for he was afraid, because he was yet a youth.": Jether refuses to obey his father's command.

Fear: Jether is afraid. Killing captured kings, even in the context of war, is a weighty act. He might have been intimidated by their royal status, their potential for retaliation (even though they were captured), or simply by the act of killing itself.
"Because he was yet a youth": This reinforces the idea that Jether lacked the experience, confidence, or perhaps the ruthlessness that Gideon expected of him. He was likely still in his teens and may not have been trained in combat or accustomed to such violence. It could also imply a degree of innocence or moral hesitation that his father, hardened by war, no longer possessed.

In essence, the verse highlights a clash between generations and perspectives:

Gideon: Represents the older generation, hardened by war and committed to exacting justice (and perhaps displaying his own power).
Jether: Represents the younger generation, perhaps less accustomed to violence, more hesitant to take a life, and possibly lacking the experience to carry out such a brutal command.

Significance:

Character Development: It reveals something about Gideon's character – his ruthlessness and his desire for public vindication. It also shows a contrast with his son, Jether.
Missed Opportunity: Jether's refusal is a missed opportunity for Gideon to publicly solidify his victory and establish his authority.
Foreshadowing: Some interpret Jether's refusal as foreshadowing Gideon's own later refusal to become king, suggesting a complex relationship with power and authority within Gideon's family.
Themes of Violence and Justice: The verse raises questions about the nature of justice, the use of violence, and the psychological impact of war on individuals and families.

It's a small verse, but it speaks volumes about power, obedience, fear, and the complexities of leadership in a violent time.