“Then they went up to Jerusalem, as the festival of weeks was close at hand. After the festival called Pentecost, they hurried against Gorgias, the governor of Idumea. He came out with three thousand infantry and four hundred cavalry. When they joined battle, it happened that a few of the Jews fell.”
They went on to Jerusalem because the festival of the weeks or Pentecost was coming up. After the festival of Pentecost that was 7 weeks after Passover, they want out to war against Gorgias. Idumea was southeast of the Dead Sea, the old Edom or Esau territory. Gorgias had only 3,000 infantry and 400 cavalry. In this battle, some Jews actually died.