And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir.
Those expressions are not the language of unbelief, but of humble enquiry. See Genesis 12:2 and Genesis 13:16. It is sweet to spiritualize. Doth not every faithful son of Abram say the same, until Christ, the promised seed, is formed in the heart?