Judges 12:3

And when I saw that ye delivered me not
Gave him no assistance against their common enemy, did not attempt to save him and his people out of their hands, but left them to defend themselves:

I put my life in my hands;
ready to deliver it up in the defence of his country; the meaning is, that he exposed himself to the utmost danger, hazarded his life in going with a few troops into an enemy's country to fight him, and so liable to lose his life; which was in as much danger, as some observe, as any brittle thing contained in the hand is in danger of falling, or of being snatched out of it:

and passed over against the children of Ammon:
took a long and fatiguing march over the land of Gilead into that of the children of Ammon, to fight with them:

and the Lord delivered them into my hand;
gave him victory over them, which showed that his cause was just, and his call to engage in it clear:

wherefore then are ye come up unto me this day to fight against me?
who rather should have come with thanks to him for the service he had done, not only for the Gileadites, but for all Israel; for had he not fought against the children of Ammon, and conquered them, they would have soon not only overrun and oppressed Gilead, but would have come over Jordan, and dispossessed the other tribes, and particularly Ephraim, as they had done already, ( Judges 10:9 ) so that it was base ingratitude in these people to come to fight against Jephthah, who had fought for them, and wrought salvation for them.