Pirkei Avot 1:2

Shimon the Righteous (HaTzadik) was of the remnants of the Great Assembly. He
used to say: "The world stands on three things - on Torah, on Avodah and on Gemilut Hasidim"

Shimon HaTzadik chose three categories on which he claims that the world stands. Putting Torah aside for a moment, we can look at what he means by Avodah and by Gemilut Hasidim. Avodah specifically refers to the sacrifices in the Temple. Shimon lived at a time when the Temple still stood and was the center of Jewish worship. The daily sacrifices as well as the sacrifices for specific reasons and times were the center of Israelite worship of G-d. But even during Shimon's time, there was more to the worship of G-d than sacrifices in the temple. The synagogue had emerged by this time and there were more local and more transcendant methods of worshipping G-d, including prayer and study of sacred text. We can see that Avodah refers not to a specific method of worshipping and serving G-d, but to a category of service that we refer to as Mitzvot ben Adam L'Makom, mitzvot between a person a G-d. All of our ritual actions, such as prayer, Shabbat, Kashrut, tefillin, and tzitzit fall into this category of worship.

The other category that Shimon identifies is Gemilut Hasidim. This category covers all of the mitzvot that are Ben Adam V'Adam, those that are between a person and another person. Commandments to care for the poor, visit the sick, welcome the guest, celebrate with the bride, and others fall into this category. Between Avodah and Gemilut Hasidim, we cover all of the commandments that G-d has given to us.

What, then, is Torah in Shimon's tri-archy? If we understand his three pillars to represent three different categories that stand apart from each other while linked through their role of sustaining the world and in their ultimate source as coming from G-d, then we need to derive a category for which Torah is the archetype or representative. One clue is in recognizing that Torah is different from Avodah or Gemilut Hasidim in that the latter categories are actions that we, humans, must take. People are responsible for performing the sacrfices, offering prayer, wearing tzitzit, leaving corners of the field for the poor, doing tzedakah and all of the other mitzvot. By contract, Torah is something is G-d's revelation to His people. Torah is G-d's action, G-d's responsibility to us.

The difference between Torah and the other two categories is that the latter categories, mitzvot that we must perform, represent finite actions. Either we perform the mitzvah or we don't. Once we have performed it, it is done and we move to the next mitzvah. The peformance of a mitzvah stands at a point in time. By contrast, Torah is an eternal revelation. According to the Midrash, Torah was created before the world was created and will exist in the World to Come.

Torah is how we know what G-d expects of us. It is the revelation of G-d's will that informs us how to perform the mitzvot that makes up the other two pillars. It is G-d's part in sustaining the world. G-d has one part in making the world exist; we have two. G-d has told us what we must do to sustain our world. It is up to us to do it.