Notably, this blessing includes wealth and power. Israel would be served by peoples and nations, and Israel's posterity would have a preeminent place among the nations.
However, there is something else. Jacob's mother had only two sons, Jacob himself, of course, and Esau. Yet, Isaac, speaking to Jacob, uses the word "sons," plural, as if Jacob had more than one brother. In fact, God's Word says nothing of Rebekah having three or more sons. This perplexes us as much as it must have perplexed Jacob when he heard these words. Why does Isaac use the language he does?
Clearly, Isaac is speaking of Abraham's extended family. The word "brethren," which is an old form of the plural of "brother," refers to all the descendants of Abraham, those through Hagar and Keturah, as well as the descendants of Esau himself. Jacob's "mother's sons" refers to all the progeny of Rebekah, falling through Jacob himself and Esau. "The blessing here raises to the idea of universal domination" (Keil and Delitzsch Commentary on the Old Testament: The Pentateuch, p. 177).
Therefore, the blessing points to future generations, not just to the lifetime of Jacob himself. Its thrust is for the Israel of a future time.
Searching for Israel (Part Two): Blessings in Faith