Genesis 12:3 . . . All the families of the earth will be blessed through you.

This promise was later repeated; clearly specifying that it would be through his offspring that this blessing to all nations would come:

Genesis 22:18 All the nations of the earth will be blessed by your offspring, because you have obeyed my voice.

The promise was further narrowed down to only one of Abraham’s children, Isaac, whom God told:

Genesis 26:4 I will multiply your offspring as the stars of the sky, and will give all these lands to your offspring. In your offspring will all the nations of the earth be blessed

Again this promise was narrowed down to just one of Abraham’s children, Jacob (Israel), to whom he said:

Genesis 28:14 Your offspring will be as the dust of the earth, and you will spread abroad to the west, and to the east, and to the north, and to the south. In you and in your offspring will all the families of the earth be blessed.

It was further narrowed down to descendants of David. In a psalm about the king (i.e. a descendent of David) we read:

Psalms 72:17  . . . Men shall be blessed by him. All nations will call him blessed.