Avot285

16:
According to the enumeration of Rambam the next trial in the series of ten which spanned the life of Abraham was his continuing lack of offspring. This was a terribly worrying test of Abraham's faith. He had left his original homeland upon the promise that he would become a great nation; immediately upon arrival in the land he was told "to your descendants will I give this land" [Genesis: 12:7]. This promise was emphatically repeated after he had separated from Lot:

And the promise had been repeated yet again during Brit Beyn ha-Betarim [Genesis 15:7].

17:
And yet, here was Abraham, at an advanced age, still childless because his beloved wife Sarah had not borne him offspring. How could the promise that he had heard be fulfilled if he had no child? Without a son he could have no progeny which could become a nation too numerous to count which would eventually take possession of the land. This is the very question that Abraham asks when told that a great reward is in store for him:

18:
Thus it was that at a certain point Abraham begins to doubt that Sarah will be the vehicle through which this promise will be fulfilled. Perhaps it is another woman who must be the mother of his nation. This must have been a great blow to Abraham's faith: Sarah had accompanied him steadfastly through all the vicissitudes that they had encountered thus far. Indeed, it was Sarah herself who suggested that perhaps she would have to become the mother of Israel by proxy; perhaps she needed a surrogate. Abraham was persuaded to cohabit with a servant of Sarah's, one Hagar from Egypt. However, Sarah was immediately filled with a sense of her own inadequacy and treated the woman so harshly that she ran away. Upon her return Hagar bore Abraham a son, Ishma'el.

19:
At this point let us jump ahead to a later trial. When, at long last, Sarah has borne Abraham a son she demands that Hagar and her son be removed from the household. Abraham is filled with sadness: Ishma'el is his son even if he is not Sarah's son. But the voice is insistent:

To be continued.

In Avot 283 I wrote: Melchizedek is a priest of the Canaanite deity El, the father of Ba'al and Ashtoret, whose special title was El Elyon, El the Supreme. Melchizedek blesses Abraham in the name of his god (thus suggesting that Abraham's success was to be attributed to El)… Abraham will have none of it, and a couple of verses later he demonstrates (and remonstrates) his steadfast faith.

Art Kamlet asks:

Why, then, do we incorporate the name El Elyon into the first verse of the Amidah?

I respond:

I do not understand Art's difficulty. Abraham himself gives his God this title when he rebuffs the congratulations of Melchizedek. He says that his success did not come from the solicitations of the Canaanite god El. Abraham raises his hand in token of a solemn oath:

Abraham emphasizes that it is Adonai who is El Elyon, and this is the reference in the Amidah.