This question is posed by the Gemara, in Masechet Shabbat (21b). Rashi explains this question to mean, “For which miracle did they institute it?” Two miracles occurred on Chanukah: the miraculous military victory – “You gave over the mighty into the hands of the weak; the many into the hands of the few” – and, secondly, the miracle of the single jug of oil. In its answer to the question of “what is Chanukah,” the Gemara chooses to tell the story of the oil:

“When the Greeks entered the Sanctuary, they contaminated all the oil… and they [the Jews] found only a single jug of oil… but it had only enough to burn for one day. A miracle occurred to it, and they lit with it for eight days… The following year, they instituted them [the eight days] and made them festivals with praise and thanksgiving.”

Seemingly, then, the festival of Chanukah was established in commemoration of the miracle of the oil. However, when we express our gratitude to Hashem in the “al ha’nissim” paragraph which we add on Chanukah to our shemoneh esrei prayer, we make no mention whatsoever of this miracle. Instead, we speak only of the military victory: “You came through for them during their time of crisis; You waged their battle… You took revenge on their behalf…” Why?

If we carefully examine the events that resulted in the war against the Greeks, we will notice that the Greek Empire had no interest in destroying the Jewish people as Haman did. Rather, they sought to have the Jews neglect the Torah and violate Hashem’s laws. They enacted decrees forbidding the study of Torah, berit mila and Shabbat observance, and they disrupted the service in the Beit Hamikdash. The war waged by the Jews against the Greeks was a spiritual one, not a physical one. The Greeks sought to “darken the eyes” of Benei Yisrael by making them forget the Torah and neglect the mitzvot.

In the end, of course, Hashem performed a miracle and the Jews defeated the Greeks. This victory was not only the triumph of the feeble over the mighty and the few over the many, but also a victory that entailed a “kiddush Hashem” – “and for Yourself, You made a great, sacred Name in Your world.”

For what reason, then, did the Gemara bring only the story of the jug of oil, and not the story of the military victory?

The Penei Yehoshua answers that the miracle served to express to the Jews Hashem’s immense love for them. Hashem loved the Jewish people to such an extent and wished to deal kindly with them, that He revealed His Shechina to them and performed this wondrous miracle.

With this in mind, we can better understand the Gemara’s discussion. The miracle of the oil was a greater miracle than that of the military triumph. Wars can be won through purely natural means, but a single jug of oil can never burn for eight days within the laws of nature. When Hashem performs a miracle outside the framework of the laws of nature, this demonstrates the greatness and importance of the miracle.

When we thank the Almighty for the miracle that occurred on Chanukah, we express our gratitude for the miracle of our salvation. But for a miracle performed only so that we can fulfill a mitzvah – such as the miracle of the oil – expressing gratitude is not the appropriate response.

What, then, is the appropriate response to this miracle, of the single jug of oil? The answer is, quite simply, that we need to go ahead and fulfill the mitzvah. For example, how do we commemorate the event of Matan Torah on Shavuot? We study the Torah we received on this day. Similarly, on Chanukah, what can we do to remind ourselves of and celebrate the miracle of the menorah? Very simple: we light candles. This is how we express our gratitude – we fulfill the mitzvah.

The candles we light publicize and remind us of the miracle of the jug of oil in the Beit Hamikdash. But acknowledging the miracle of the oil does not suffice. By contemplating this overt miracle, our eyes will be opened to recognize the other miracles – “and increase the praise of God and thanksgiving to Him for the miracles He performed for us.”