In Bereshit 12:3 HaShem tells Avram: וְנִבְרְכוּ בְךָ, כֹּל מִשְׁפְּחֹת הָאֲדָמָה - in thee shall all the families/households of the earth be blessed.
While in Bereshit 18:18 it says: וְנִבְרְכוּ-בוֹ,כֹּל גּוֹיֵי הָאָרֶץ - and all the nations of the earth shall be blessed in him.
At first sight I thought they meant the same thing, but then the differences between these two verses stood out: One talks about Mishpechot, while the other talks about Goyey, one talks about Ha'Adamah while the other talks about Ha'Aretz.
Whats the difference for, what does it imply and what is the nuance between these two verses. For they don't seem to refer to the same thing.