Genesis 15:3

And Abram said, Behold, to me Thou hast not given a son; and, behold, the manager of my house will be my heir.

בן ביתי יורש אותי, even though, in the end, You will give me biological offspring, as You have said in 12,7 לזרעך אתן את הארץ הזאת, “I will give this land to your descendants,” such children will only be minors at the time, so that my servant Eliezer will have to raise them and guide them, in effect being my heir.

הן לי לא נתת זרע, although You have said to me “I will make you into a great nation and I will make your descendants as numerous as the dust of the earth” (12,2) When Avram said all this to G’d, it did not cross his mind that G’d might have deceived him, lied to him, and that this was why the promise had not come true. He may have thought of one of two reasons being the cause why the promise had not been fulfilled. 1) that he had committed some sin after G’d had made the promise, so that the premise upon which the promise had been based was no longer valid. 2) or, he thought that the seed G’d had spoken of was a reference to some other family member, people carrying many of the same genes. The word זרע does appear in such a sense in Esther 10,3 where Mordechai is described as דובר שלום לכל זרעו, “interceding on behalf of all his seed.” If Mordechai had interceded only on behalf of personal children and grandchildren, this would hardly have been worth mentioning, certainly not worth praising him for. Basically, Avram wanted G’d to know that if G’d had meant that the definition of the word זרעך as mentioned in 12,2 was only in the most general sense, such as in Esther 10,3, then he, Avram, would not consider this reward as something special seeing G’d had not seen fit to make his wife conceive offspring from his seed.