http://revach.net/article.php?id=4853

Section: Moadim   Category: Chanukah
The Bais Yosef's Kashya - A Celebration Of Bitachon In The Face Of Victory

The Bais Yosef asks why do we light the Menora eight nights, if they found one jug of oil then only the other seven were a Nes? The Lahavas Dovid answers as follows.

The Chashmana'im won a great battle over the Yevanim. Typically after a victory, no matter how miraculous, there is a tendency to believe that human efforts were the cause of victory, "Kochi V'Otzem Yadi". Especially in this case the Chashmana'im had what to be proud of. Yet it wasn't so. The Chashmana'im attributed there victory to Siyata Dishmaya and took no credit for themselves.

It was this bitachon that prompted them to use the lone tahor pach shemen. They knew that they would eventually need to use shemen that was tamei since they did not enough to last for eight days. Yet they chose to light what they had, and have faith that Hashem will work something out for them, just like He did in the war. It is this bitachon that we celebrate when we light the first night's candle.