The question is about Gn 15:5, which is God's response to Abraham's concern that he has no children. Basically God is saying, don't worry, you'll have kids - plenty of kids! That's the simple - pshat - meaning of the verse.
To go deeper, it is clear to me that God's answer here should be interpreted as referring to all of Abraham's descendents, not only the lineage of Jacob.
First of all, the passage in itself sounds like hyperbole - count the stars if you can count them" seems to mean simply a vast number. Indeed, while there are 5,000-9,000 discernible stars in the sky, when one looks at the Milky Way, the number of stars does seem uncountable.
Yet the question remains - for 10 million is a lot, but surely not uncountable!
Who are to be counted as his descendents? Gn 17:5 provides a clue - "I have made you a father of many nations."
How many is "many"? According to rabbinic tradition, this refers to the whole world, because the entire world is destined one day to follow in Abraham's footsteps. So 15:5 is not referring only to the lineage of Jacob.
[As an aside (not a proof, just an interesting fact), the latter verse is where God changes his name from Avram to Avraham. Avram means "father of Ram", i.e., Aramaia. Avraham means "father of many" but could also be read as "father of raham"; according to the basic method of gematria (numerology) this could be read as "father of 245".
Now, if you go by the UN, there are fewer than 200 nations. But if you go by 2-digit internet country codes (see http://goes.gsfc.nasa.gov/text/web_country_codes.html) there are about 243. Therefore, all we need is a couple more countries to split into two for God's promise to Abraham to be fulfilled.]