What is the significance of the comparison of Yisrael to the dust of the earth?
Rashi (in the original print): Hashem is predicting that Yisrael will ultimately go into Galus - scattered across the face of the globe like the dust of the earth.
Rashi #2 (Ibid.): Jusr as, if there would be no earth there would be no trees and no produce, so too, if there would be no Yisrael, the world not not exist. 1
Targum Yonasan: 'Hashem promised to make Avraham's children numerous like the (particles of) dust. 2
Rashi (Ibid.): As the Torah writes in Toldos, 26:4 'Vehisabarchu be'Zar'acha Kol Goyei ha'Aretz. In the days of Mashi'ach however, Yisrael will be compared to sand (se 49:10) which grinds (Makheh) the teeth of whoever chews it, because then the entire world will fall and be ground, as the Torah writes there (in connection with Mashi'ach) "ve'Lo Yikhas Amim".
Conforming to the simple explanation og the Pasuk.
QUESTIONS ON RASHI
Rashi writes: "'That if a man can count...' - Just as it is impossible for dust to be counted...." What is Rashi explaining?
Gur Aryeh: "If" is usually a conditional statement, or indicates doubt. Here it is used rhetorically; surely it is not possible.