In Parshat Ki Tavo, Moshe commands Bnei Yisrael to set up stones when they cross into Eretz Yisrael on which they must write the words of the Torah. He states that this copy of the Torah must be written specifically in stone: “You shall inscribe on the stones all the words of this Torah” (27:8). Why did Hashem command us to make these monuments out of stone as opposed to other materials?
There is a very famous story about Rabi Akiva that while walking through his fields one day, before he had learned much Torah, he noticed a rock with a hole in it. Under closer examination, he saw tiny drop of water dripping onto the stone. Over the years, these drops of water bore a substantial hole through the rock. Rabi Akiva, an illiterate forty-year-old man, realized that if something as soft as water can puncture something as hard as a rock (given enough time), surely Torah, too, can penetrate the soul of a Jewish person. Rabi Akiva went on to become one of the greatest Talmidei Chachamim to walk the face of the earth.
With this story in mind, we can understand why Moshe commanded that the Torah be written specifically on stone. He wanted to make sure that people would remember that even if a person is not capable of easily grasping a particular Daf of Gemara or Halacha or Perek of Tanach, he must still continue to strive to become more of a Talmid Chacham because it will always affect him spiritually in a positive way, just as water is famous for doing to stone.
--Adapted from a Dvar Torah in Vedibarta Bam