In this week's Torah portion, Ki Tisa,

In this week's Torah portion, Ki Tisa, we read that when Moses came down from Mount Sinai with the Tablets of the Law he saw the Jewish people sinning with the Golden Calf. With everyone watching, he threw the holy Tablets down and broke them. The Midrash relates that Moses later regretted what he had done. G-d said to him, "Do not be aggrieved. The first Tablets contained only the Ten Commandments, but the second Tablets I will give you will have much more! For together with the second Tablets the Jewish people will receive halachot (laws), midrashim and agadot (homiletic interpretations), and the entire Oral Torah!"Why didn't G-d include these things when He gave the first set of Tablets?
To explain: In order to receive G-d's Torah, a person must be humble. Only through humility does he become an appropriate vessel to contain it.
This is what we say in our prayers: "And may my soul be like dust to all; open my heart to Your Torah." When we feel ourselves to be as lowly and humble as the dust, our hearts are opened to accept the Torah.
At Mount Sinai, G-d chose the Jewish people from among all the nations of the world, "lifting us up above all tongues." Thus the Jewish people felt themselves exalted; they were filled with self-importance and lacked the modesty and humility which is necessary to receive the Torah.
When Moses broke the Tablets before their eyes the spirit of the Jewish people was also broken. Profoundly humiliated, their hearts became filled with a sense of their own lowliness; they became "like the dust of the earth."
At that moment the Jews became worthy of receiving the entire Torah - not only the Ten Commandments, but all of the Torah's various aspects and levels!
In fact, as Rashi, the foremost Torah commentator, notes, G-d praised Moses for what he had done. "More power to you for having broken them!" G-d declared. G-d thanked Moses for having broken the first Tablets. For Moses' action caused the Jewish people to be humbled, and as a direct result, worthy of receiving the entire Torah.
In this light we can better understand the Talmud's statement that the fragments of the first Tablets were kept inside the Ark in the Holy Temple together with the intact second set.
Why were the broken fragments included? To remind us that we cannot receive G-d's Torah without humility. Arrogance and pride are emotions that preclude a person from being a proper vessel. When Jews bear this in mind, our hearts are opened, and we can receive G-d's Torah.

Adapted from Likutei Sichot of the Rebbe, Volume 26