Charles Spurgeon Commentary Genesis 12:2-3

"and I will make of thee a great nation, and I will bless thee, and make they name great; and be thou a blessing; and I will bless them that bless thee, and him that curseth thee will I curse: and in thee shall all the families of the earth be blessed." — Genesis 12:2-3 (ASV)

There, you see, was the missionary character of the seed of Abraham, if they had but recognized it. God did not bless them for themselves alone, but for all nations: In thee shall all families of the earth be blessed.