Jephthah: The consequences of degenerate religion

Commentator Barry Webb summarizes well the story of Jephthah:

At its deepest level the story of Jephthah is about the tragic consequences that follow when religion degenerates into bargaining with God. It shows us how deeply the Israelites of Jephthah’s day, including Jephthah himself, had begun to misconstrue their relationship with God. Indeed it was only because of the Lord’s great mercies that they were not left to the fate they so richly deserved.

And Lamentations 3:21-23 give a great summary of the Lord's great mercies:

21 But this I call to mind, and therefore I have hope: 22 The steadfast love of the Lord never ceases; his mercies never come to an end; 23 they are new every morning; great is your faithfulness. - Lamentations 3:21-23