ארץ אשר אבניה ברזל ומהרריה תחצב נחשת ... (ח-ט)
The Rambam writes in Hilchos Melachim (5-10): “Great Rabbis would kiss the ground of Eretz Yisroel, and kiss its stones, as well as roll in its dust as it states, ‘Because your servants wanted its stones and begged for its dust.’” Some wonder how the great rabbis knew when they had reached the Holy Land in order to kiss the ground and stones? After all, for thousands of years, there were no defined borders where one could easily discern that he had left a neighboring territory and had now definitively entered the Land of Israel.
Tosfos in Kesubos (קיב.) quotes a Medrash Tanchuma: “When Rav Chanina Hagadol went up from Bavel, he wished to know when he had entered Eretz Yisroel. He would pick up stones and weigh them. If they were light, he knew he hadn’t yet arrived. As soon as the stones became heavier, he announced, ‘These must be the stones of Eretz Yisroel.’ He then kissed them and recited the posuk, ‘Because your servants wanted its stones and begged for its dust.’” In fact, states the Medrash Talpios, this was exactly how the early Chassidim (חסידים הראשונים) would determine where the border of Israel was; by feeling the weight of each stone.
Chacham Rabbeinu Chayim Yosef Dovid Azulai zt”l (Chida) has an alternate understanding of the stones of Israel. The first letters of "אבניה ברזל ומהרריה תחצוב" spell out "אבות". The stones - the foundation of the Land - are "ברזל" - Bilhaa, Rochel, Zilpah and Leah - the four Matriarchs. "הרים" - the mountains refer to the Patriarchs, as it says, “Leaping upon the mountains” (שה"ש ב-ח) - mountains refer to the Avos. In the merit of our holy Forefathers and mothers, the Jewish people will control "נחשת" - a reference to the snake (נחש) embodied by Esav and the oppressors of Klal Yisroel.