Gen 15:4-5 4 And behold, the word of the LORD came to him, saying, “This one shall not be your heir, but one who will come from your own body shall be your heir.” 5 Then He brought him outside and said, “Look now toward heaven, and count the stars if you are able to number them.” And He said to him, “So shall your descendants be.”

This promise to Abraham is explicit. God did not promise him an adopted child or a cousin; He is promising Abraham a son who will come from his own body. Then God patiently gave Abraham an astrologica object lesson, telling him to “Go outside – look up – can you count the stars?” God reminds Abraham that He put all those stars in place; He is the creator of heaven and earth. Is anything too hard for a God like that – including giving Abraham a son from his own body, or descendants as innumerable as the stars?

God did not respond to Abraham’s weak faith with anger or rebuke; he very patiently reminded him of his immeasurable power and renewed his promise to Abraham once again.