Why is Isaac called Abraham's only son? [duplicate]

Question

This question already has an answer here:

• Why does the Scripture say that Abraham sacrificed his “only-begotten son”? 2 answers

Continuing the response to the meta call for contradiction.

In Genesis 22, we find the following passage:

And it was after these events that the God tested Abraham; and said to him "Abraham", who replied "Here I am." And said "Take now your son, your only, which you have loved, Isaac, and go you to the land of Moria, and raise him up there as an offering, on one of the mountains, which I will tell you."

Why is Isaac called Abraham's only son, when Ishmael would be the firstborn? It is traditional to enumerate the sons of the slave wives as belonging to the proper wife (see later Genesis regarding the sons of Jacob through slaves belonging to Leah/Rachel--- Dan is still the first generated of Rachel, even though he is born by Bilha), so Hagar's son would count. But in this verse, it is as if Abraham only has one son.

Answer 1

As with all other textual inconsistencies, this is completely resolved by the documentary hypothesis. Chapter 22 is an Elohist narrative, and in this chapter we learn that Ishmael is either absent from the Elohist narrative or is second born. Either that, or as the Muslim tradition upholds, later redactors replaced Ishmael with Isaac in the story, to make the lesson of the story, abolishing child sacrifice, more appropriate for the descendents of Isaac.

Answer 2

Ge 16:15 And Hagar bare Abram a son: and Abram called his son’s name, which Hagar bare, Ishmael.

Ge 16:16 And Abram was fourscore and six years old, when Hagar bare Ishmael to Abram.

Ge 17:5 Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee.

Ge 17:19 And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him.

This is classic prophetic riddle:

Ishmael was born to Abram, Isaac was born to Abraham. Abraham was a new man and had an only son.

Also Only יחידכ not only means 'only' but 'darling'. Isaac was clearly Abraham's darling son. Hidden in יחידכ is יחי which means 'he shall live'. Isaac was the son of promise and God declared 'he shall live' even as he asked Abraham to sacrifice him.