The Torah commanded Bnei Yisrael to write the words of the Torah on stones on the day they would enter Eretz Yisrael "so that they will come into the Land" (Devarim 27:3). Although the mitzva was to be done when they entered the Land, what does it mean that it should be "so that they will come..."? The Ramban says that it was in the merit of the Torah that Bnei Yisrael were able to enter the Land. Rabbeinu Bachyei adds onto that this is why the Rabbis required us to mention thanks for the Torah during the beracha of Birkat Hamazon that is devoted to Eretz Yisrael.
As we know from bentching and as the gemara (Berachot 48b) says, right next to our thanks for the Torah comes our thanks for brit milah. According to Rabbeinu Bachyei’s thesis, is this mitzva too related to Eretz Yisrael specifically? Looking at Sefer Yehoshua, where the entrance to the Land is chronicled, we see the following chain of events. Bnei Yisrael fulfilled the command of writing the Torah on stones upon crossing the Jordan. The next thing mentioned is a mass fulfillment of brit milah, as most of the men entering Eretz Yisrael had not had one in the desert. Both of these events occurred on the 10th of Nisan. The next thing mentioned is the first Korban Pesach in Eretz Yisrael.
There is much discussion in Chazal and among commentaries as to how it could be that most of Bnei Yisrael did not have a brit milah when they were under Moshe’s tutelage. The explanation is that because of a basically legitimate fear of danger under conditions in the desert, most refrained from milah. It still seems strange that considering all the miracles in the desert, Hashem could not have assured the people that they could proceed safely with a brit, yet on the very day they entered a new and potentially hostile land they were free to do so. The Radak says that the timing of the mass britot in Yehoshua’s times coincided with the upcoming Korban Pesach. However, the Yalkut Shimoni (Yehoshua 15) says that there was a message to Bnei Yisrael involved in this immediate undertaking. "Do not think you can enter the Land and keep the foreskins." The Yalkut points out that when Avraham Avinu was first commanded to do the brit milah, it was in the context of the promise that his descendants would receive Eretz Yisrael.
So we have a strong indication that brit milah and the Torah (in general, and the writing on stones upon entering Eretz Yisrael specifically) are merits that are connected to success in the Land. Both attach a physical sign of an important concept related to the matter. Milah reminds us that the Jewish body must be used in a holy manner as part of a covenant with Hashem. Eretz Yisrael is to be used as a base for the national fulfillment of the Torah. These mezuzah¬-like stones on the gateway to the Land set the tone for what needed and needs, now and in the future, to be proper use of the national homeland.