When the righteous multiply in the world, good things multiply with them. This is Aggadat Bereshit's reading of "When the righteous are many, the people rejoice" (Proverbs 29:2). Not "when the powerful rule wisely" or "when the laws are just" — when the righteous are numerous. The midrash traces this through Moses's directive to Israel: "So that it may go well with you and your children after you forever, when you do what is good and right in the sight of the Lord your God" (Deuteronomy 12:28).
The earth itself responds. "The earth is filled with the abundance of God's waters" (Psalm 65:10) — rain, the rabbis said, falls in proportion to Israel's righteousness. Not as mechanical reward, but as the natural consequence of a world properly aligned. When the people keep covenant, the covenant's blessings flow. When they don't, the blessings withdraw. Famine is not random. Neither is abundance.
The rabbis were careful not to make this into a simple formula. The righteous sometimes suffer; the wicked sometimes prosper. But in the aggregate, over generations, the pattern holds: a world with more righteous people in it is a world where more children rejoice. This is the argument the midrash builds from Jacob's household — a family that stayed together through betrayal and loss and reunion, and on the far side of all of it, multiplied into a nation.