The “surface” meaning of a text is known as a peshat. In other words, a text means what it says—whether or not it is intended literally or figuratively. When God called Abram to leave his own “country,” God promised him (among other things) that He would make of Abram a “great nation” (Gen 12:1-3).
How do we know that God intended to “raise up” a “flesh and blood” people from Abraham—a physical people (Israel) through whom He would accomplish His redemptive purpose in the Olam HaZeh (this world)? It’s simple!
After the defeat of the kings that had taken Lot captive, Abraham reminds God of His blessing, “O Sovereign Lord, what can you give me since I remain childless and the one who will inherit my estate is Eliezer of Damascus?” (Gen 15:2). Abraham’s question is prompted by his understanding of God’s promise, i.e., that it referred to physical, promised descendants. And apparently, that is the way God intended it too, for He responds, “This man will not be your heir, but a son coming from your own body” (Gen 15:4) In fact, God “took him outside and said, “Look up at the heavens and count the stars … so shall your offspring (or “seed”) be” (Gen 15:5).
Perhaps this is what prompted Paul to say, “For no matter how many promises God has made, they are ‘Yes’ in (Messiah). And so through him the ‘Amen’ is spoken by us to the glory of God” (2Co 1:20 [NIV]). We can count on God to be faithful to His Word!