Sforno on Genesis 28:14/ספורנו על בראשית כ״ח:י״ד

1והיה זרעך כעפר הארץ, ופרצת, after your descendants will have multiplied so that they are as the dust of the earth, numerically speaking, you will spread out. The expression is to be understood as similar to Isaiah 51,23: ותשימי כארץ גוך וכחוץ לעוברים, “so that you made your back like the ground, like a street for passers by.” Precisely when the Jewish people will have reached a seeming low point in their collective experience (downtrodden by the Egyptian taskmasters, or in later exiles) they will expand and become powerful in a measure never before seen on earth. ימה וקדמה צפונה ונגבה, when that time arrives Bileam’s prophecy in Numbers 24,17 וקרקר כל בני שת, “it will smash the foundation of all mankind.” The final redemption of the Jewish people will come after they have suffered the low point in their history. (Compare Sanhedrin 95: “if you see a generation experiencing so many persecutions and setbacks that it appears a raging river is inundating them, wait for the ending for the prophet Isaiah in his description of the redemption writes of it immediately after having described the very opposite in chapter 59, 19-20”)

2ונברכו בך כל משפחות האדמה ובזרעך, the same type of blessing mentioned in Isaiah 61,6 i.e. because you will then be known and revered as the priests of the Lord, they will receive their Divine blessing through you.