To know the answer for why Hanukkah is celebrated, we would have to trace its history. The history of Hanukkah dates back to 165 BC. During that period, the land of Judea was ruled by Antiochus, a Syrian King. The King ordered the Jewish people to give up all their rituals and beliefs and start worshipping Greek Gods. The Greek soldiers also forced them to bow in front of a Greek God's idol and eat the meat of a pig, which was strictly against the Jewish Law.
Out of fear, some Jews obeyed the King's orders while the rest of the
Jewish people were very anger and decided to fight back. This gave birth
to a rebellion. The aggressive Jewish army fought for their religious
freedom. The result was in favor of the Jews. They conquered the Greek
soldiers and succeeded in restoring the Holy Temple in Jerusalem.
Hanukkah is celebrated to commemorate the victory of Judah Maccabee's
Jewish army over the Greek soldiers and the rededication of the Holy
Temple in Jerusalem. Hanukkah marks the religious freedom of the Jewish
community. The festival pays tribute to the Miracle of Oil, the purified
oil that was worth lighting candle for only one day, but miraculously
lit the candles on the Menorah for eight days continuously.