So, Jephthah is a man from a long, long time ago in a place called Israel. He was an important leader of his people because he was a great warrior and very strong. But, Jephthah had a sad past because when he was younger, his family kicked him out and he had to live all alone by himself.
One day, his people were going to war against another group of people, and they needed Jephthah to help them fight. But, Jephthah wasn't sure if he should help because he was still really upset about being kicked out of his family. He prayed to a god for help, and promised that if he won the war, he would sacrifice whatever came out of his house first when he returned home.
Jephthah ended up winning the war, but when he went back home, the first thing that came out of his house was his daughter. Jephthah was very sad and didn't want to hurt his daughter, but he had promised the god he would sacrifice whatever came out of his house first. So, Jephthah did what he promised and sacrificed his daughter.
It's a very sad story, but it shows that sometimes people make promises that they shouldn't and that can have very bad consequences. It's important to think very carefully before making a promise and to make sure it's something you can keep without hurting anyone.