In the Chanuka story, the flask of pure olive oil was enough to last for one day. Therefore, only the 7 other days that the oil remained lit was a miraculous. So why do we light eight candles and not seven?

Thank you for your question. The most famous book that addresses this issue was written in Hebrew and is called Ner L’mai’ah. The author supplies 100 (!) answers to the above mentioned question.

I will supply you with four of these answers:

1) 1/8 of the oil burned each day, meaning that each day had a miracle.
2) One day commemorates the military victory.
3) One day is for the miracle of finding the oil.
4) One day is to celebrate the annulment of the decrees that the Greeks imposed upon the Jews (such as forbidding Torah study, circumcision, etc).