Jephthah knew his history. He knew how God delivered time after time. He was able to quote the battles. To find strength from the victories. To be bold when faced by the enemy.
Not because he lived through all of those battles. Most of what he referenced happened three hundred years prior to the battle he was facing.
But because he knew that The Lord had always been faithful to his people he put his confidence in the one true God.
The Bible gives us an entire collection of accounts where God was faithful to his children. Get into his word. Study it out. Be strengthened by what it has to offer.
Jesus has never failed his chosen ones. He won’t begin with you. Find hope in his Word.