What does Judges 15:3 mean?

Samson's would-be father-in-law explained that he gave away Samson's bride to another man (Judges 15:1–2). That might not have been entirely legal; Samson wasn't aware and seems not to have been repaid any bride-price which had been paid. Her father was not completely unreasonable, however. He assumed Samson had abandoned the woman, leaving her vulnerable and socially destitute (Judges 14:20). Now that Samson has returned, the man offers Samson his younger daughter. We're not sure what reputation Samson had at this point, but it's possible he was already known as a brawling, violent man (Judges 14:10–11).

Despite this attempt at making peace, Samson seems to immediately reject marrying the younger sister. All that matters is something he wanted has been denied (Judges 14:1–3). He believes he has been thoroughly mistreated. First his bride betrayed him by revealing his unfair secret (Judges 14:14–17). Then, her father swindled him by giving her to a rival after the wedding had already taken place.

Samson's vengeful nature is demonstrated in the fact that he doesn't merely explode in anger. Rather, he says something deeply ominous. After the first treachery, he took the time to travel to another city and kill thirty Philistines (Judges 14:19). The comment he makes here is doubly concerning. First, it suggests Samson felt his prior killing of Philistine men was unjust. Second, it suggests that he plans to bring mayhem once again.

When considering these events, it's crucial to recall the Lord's plan for Samson's life. He has been set aside to "begin to save" Israel from Philistine oppressors (Judges 13:5). His volatile nature is meant to provoke a conflict which will eventually end in Israel's rescue (Judges 14:4). That Samson seems motivated purely by revenge, not piety, doesn't change that aspect of God's plan. Now that Samson feels personally offended by the Philistine people, he is ready to cause destruction.