What was the difference between the first set of Luchot that were carved by G-d and the second set of Luchot that were carved by Moshe?
Rav Saadiah Gaon suggests that the second Luchot were heavier than the first. This seems very strange and in fact the Ibn Ezra strenuously objects to this idea. However, the Neztiv in Haamek Davar explains Rav Saadiah Gaon based on a Midrash.
The Midrash says that Moshe was upset after breaking the Luchot. G-d tries to cheer Moshe up by saying that the first Luchot only had upon them the 10 commandments while the second Luchot have on them the Halachot, Midrash, and Agadot. The Midrash explains elsewhere that at Sinai Moshe was given over the entire Mikra, Mishna, Talmud and even that which the distinguished student will say in front of his Rebbe. How could Moshe be given novel concepts in Torah that were not even thought up yet and how could this be written down on the Luchot?
The Netziv explains that when the Jews were given the first set of Luchot they were given the whole Torah on a silver platter. G-d gave them Torah together with explanations of the pesukim from Moshe Rabbenu. They were not given the ability to make up Chidushim, novel ideas based on their personal Limud Torah. This could only be done using the 13 rules for Drashot from the Torah and using the Socratic method found in the Gemara. These rules and methodologies were not contained in the first Luchot. Rather, the oral law was only lists of Halachot passed down from Moshe. When the Jews faced new situations they could only discover what to do by comparing these new situations to older situations contained in the Torah.
With the second Luchot every student was given the ability to develop novel chidushim in Halacha based on the 13 rules of Torah Drashot and the questioning style of the Talmud. This opened up whole new doors of learning for every student. Torah went from being a rote transmission of facts to being a joint quest between the Torah student and G-d with the goal of developing new ideas from the Torah. This is why Moshe had to carve the second set of Luchot. The Halachot derived using the Talmudic rules transmitted with these Luchot were a partnership between Man and G-d just like these Luchot were written by Man based on the word of G-d.
The reason for this new method of learning contained within the second set of Luchot was the sin of the Egel. The Chet Ha-egel laid the foundation for the later sin of the spies and the later sins that would ultimately lead the Jews into exile spreading Jewry throughout the diaspora. In galus, a stale transmission of facts was not enough. Torah had to become a dynamic living document around which the people could devote their energies during the long exile. The Talmud hermeneutics or Pilpul Shel Torah kept the Jews together as a nation and transmitted the teachings of Torah to future generations. Because the second set of Luchot contained the potential for all of this added learning they were heavier than the first. The first Luchot written with the hand of G-d had greater Kedushah, but the second Luchot contained the greater ability for Chidushay Torah. It is this ability to develop novel Torah concepts that makes Torah learning fresh and vibrant to this very day.
