Koh Yihyeh Zarekha: So shall your seed be

In Lekh Lekha we read:
After these things the word of the Lord came to Avram in a vision, saying, Fear not, Avram; I am your shield, and your reward will be great.
And Avram said, Lord God, what will you give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?
And Avram said, Behold, to me you have given no seed; and, lo, one born in my house is my heir (i.e.Yishma’el).
And, behold, the word of the Lord came to him, saying, This shall not be your heir; but he who shall come forth from your own bowels shall be your heir.
And He brought him outside, and said, Look now toward heaven, and count the stars, if you are able to count them; and He said to him, So shall your seed be.
And he believed in the Lord; and he counted it to him for righteousness.
(Beresihis 15:1-6)

The peshat is that Avram went out and looked at the stars and saw that God promised him that his progeny would be innumerable like the stars.

R. Meir Shapiro of Lublin asks:
Why did Hashem say va’yo’mer, He said, twice?

Because when Avram went out he literally started to count the stars – 1, 2, 3…10 …100…10,000 etc. So, at that point, when Hashem sees Avram counting, another va’yo’mer is warranted and Hashem then says to Avram:
Koh Yihyeh Zarekha, So shall your seed be. May they also be so literal, pure and obedient as you are in following my commands even when the task seems impossible. This foretells the na’aseh v’nishma’ aspect of the character of ‘am yisra’el.