A curious Rashi towards the beginning of parshat Vayeitzei can open our eyes to some of the poetry in Yaakov’s prophecy.
The pasuk (Bereishit 28):
And behold, the Lord was standing over him, and He said, "I am the Lord, the God of Abraham your father, and the God of Isaac; the land upon which you are lying to you I will give it and to your seed.
יג וְהִנֵּה ה נִצָּב עָלָיו וַיֹּאמַר אֲנִי ה אֱלֹהֵי אַבְרָהָם אָבִיךָ וֵאלֹהֵי יִצְחָק הָאָרֶץ אֲשֶׁר אַתָּה שֹׁכֵב עָלֶיהָ לְךָ אֶתְּנֶנָּה וּלְזַרְעֶךָ:
And the Rashi:
upon which you are lying: (Chullin ad loc.) The Holy One, blessed be He, folded the entire Land of Israel under him. He hinted to him that it would be as easily conquered by his children (as four cubits, which represent the area a person takes up [when lying down]). [From Chullin 91b]
שכב עליה: קיפל הקב"ה כל ארץ ישראל תחתיו, רמז לו שתהא נוחה ליכבש לבניו:
I do not think that Rashi believes that the peshat is that there was this astonishing miracle* for the simple purpose of conveying this hint about the ease of conquering the land. Even though there are miracles abounding in Rashi’s interpretation, of the kefitzat haderech, folding up of the path, to get Yaakov places, or of multiple stones coalescing into a single large stone. He presents us with a derasha, which he either believes to be historical or ahistorical, to teach us some message.
There is, however, an irregularity in this text which the midrash picks up upon. The word eretz serves two purposes in Biblical Hebrew. It refers to ground, that is to dirt, and it refers to a country.
And the word seems to be deliberately used for both purposes here. Hashem specifies the eretz upon which Yaakov sleeps. This is a concrete piece of ground, for cubits. But it would be silly to tell Yaakov that He is granting him those four cubits of ground, to him and to his descendants. Obviously it is referring to the country**.
This is then a more poetic prophecy that other Divine promises. It either uses the word eretz in both senses, or it is a type of synecdoche (using a part to refer to the whole). Why do this? It is emphasizing the humble state of now and contrasting it with the eventual end state. Yaakov had fled and was on his way to Charan, with little in the way of earthly possessions. (This is not just the midrash about Elifaz stealing his wealth, but in the pesukim themselves. For instance, where he says in Vayishlach “for I passed over this Jordan with only my staff, and now I have become two camps.”) He is in the wild, unprotected, and sleeping on the bare ground. And now Hashem appears to him and is nitzav upon him, guarding him, and guarantees that he will guard him everywhere he will go. And so Hashem tells him that this very bare ground upon which he sleeps, and indeed the entire country it is connected to, will belong to him.
The same poetry is present in the next pasuk, and if not for this midrash, we might have missed it:
And your seed shall be as the dust of the earth, and you shall gain strength westward and eastward and northward and southward; and through you shall be blessed all the families of the earth and through your seed.
ידוְהָיָה זַרְעֲךָ כַּעֲפַר הָאָרֶץ וּפָרַצְתָּ יָמָּה וָקֵדְמָה וְצָפֹנָה וָנֶגְבָּה וְנִבְרְכוּ בְךָ כָּל מִשְׁפְּחֹת הָאֲדָמָה וּבְזַרְעֶךָ:
Why the dust of the earth? It is again riffing on the fact that he is sleeping on the bare ground, made of dust.
One additional thought: Dust is plentiful, and beyond counting, so the standard understanding of “numerous” works here. But dust is also not rooted. When the wind blows, it will blow that dust in all directions, westward, eastward, northward and southward. And in such scattering, all the clans of the adama (ground, country) shall be blessed, as your influence and progeny spreads.
* Actually, since this is occurring in his dream, so it need not even be a miracle. It can be a miraculous dream-event, in which he imagined that Hashem folded up the earth.
* See Haksav veHakabbalah, who notes that saying, on a peshat level, the land you sleep upon need not be the land directly beneath you, but surrounding you. Perhaps. I think this is deliberate poetic use.