Abraham sacrificed his ONLY son

Abraham sacrificed his ONLY son - Gen 22:2

Why did God ask Abraham to sacrifice his ONLY SON, when in fact it was his SECOND SON Born to him? ....Would you happen to know what the original Hebrew text or any NT references really say in that spot where the English words say "ONLY" Son?

The main text is as follows:

Gen 22:2 ESV He said, "Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you."

In Gen 22:2 the Hebrew word for only son is yachiyd.

BDB Definition: 1) only, only one, solitary, one (adjective) 1a) only, unique, one 1b) solitary 1c) (TWOT) only begotten son 2) one (substantive)

The word "only" is confirmed by a NT text:

Heb 11:17-18 ESV By faith Abraham, when he was tested, offered up Isaac, and he who had received the promises was in the act of offering up his only (monogenes) son, (18) of whom it was said, "Through Isaac shall your offspring be named."

The Thayer definition of monogenes is:

Thayer Definition: 1) single of its kind, only 1a) used of only sons or daughters (viewed in relation to their parents) 1b) used of Christ, denotes the only begotten son of God

The LXX has "the beloved one" rather than "only son" (http://www.ecmarsh.com/lxx-kjv/Genesis/gen_022.htm, see also Tekton).

To understand this question we first of all need to read the promises of God to Abraham. God's promises would be fulfilled through Abraham's offspring. The promises become more specific as we go through Genesis.

Gen 12:2 ESV And I will make of you a great nation, and I will bless you and make your name great, so that you will be a blessing.

Gen 12:7 ESV Then the LORD appeared to Abram and said, "To your offspring I will give this land." So he built there an altar to the LORD, who had appeared to him.

Gen 13:14-16 ESV The LORD said to Abram, after Lot had separated from him, "Lift up your eyes and look from the place where you are, northward and southward and eastward and westward, (15) for all the land that you see I will give to you and to your offspring forever. (16) I will make your offspring as the dust of the earth, so that if one can count the dust of the earth, your offspring also can be counted.

Gen 15:1-6 ESV After these things the word of the LORD came to Abram in a vision: "Fear not, Abram, I am your shield; your reward shall be very great." (2) But Abram said, "O Lord GOD, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?" (3) And Abram said, "Behold, you have given me no offspring, and a member of my household will be my heir." (4) And behold, the word of the LORD came to him: "This man shall not be your heir; your very own son shall be your heir." (5) And he brought him outside and said, "Look toward heaven, and number the stars, if you are able to number them." Then he said to him, "So shall your offspring be." (6) And he believed the LORD, and he counted it to him as righteousness.

Gen 15:13 ESV Then the LORD said to Abram, "Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for four hundred years.

In Gen 16, we see how Abraham and Sarai take things into their own hand to have children. A similar thing happens in the marriage of Jacob and his two wives Rachel and Leah, only this time they are legitimate children (all Jacob's sons make up the twelve tribes including the sons of his concubines).

Gen 16:1-4 ESV Now Sarai, Abram's wife, had borne him no children. She had a female Egyptian servant whose name was Hagar. (2) And Sarai said to Abram, "Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children by her." And Abram listened to the voice of Sarai. (3) So, after Abram had lived ten years in the land of Canaan, Sarai, Abram's wife, took Hagar the Egyptian, her servant, and gave her to Abram her husband as a wife. (4) And he went in to Hagar, and she conceived. And when she saw that she had conceived, she looked with contempt on her mistress.

The angel of the Lord also promises to make Hagar's offspring into a great multitude.

Gen 16:10 ESV The angel of the LORD also said to her, "I will surely multiply your offspring so that they cannot be numbered for multitude."

In the next chapter, God makes it clear that his promises to Abraham, would be fulfilled through Isaac not Ishmael.

Gen 17:18-21 ESV And Abraham said to God, "Oh that Ishmael might live before you!" (19) God said, "No, but Sarah your wife shall bear you a son, and you shall call his name Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him. (20) As for Ishmael, I have heard you; behold, I have blessed him and will make him fruitful and multiply him greatly. He shall father twelve princes, and I will make him into a great nation. (21) But I will establish my covenant with Isaac, whom Sarah shall bear to you at this time next year."

The point is that it was through Isaac not Ishmael that God's promises were made and would be fulfilled. God would establish his covenant through Isaac, born of Sarah, not Ishmael born of the slave woman. Note that God also blessed Ishmael. Abraham's line would be preserved through Isaac not Ishmael. But also God would make a nation through Ishmael because he was Abraham's son.

Gen 21:12-13 ESV But God said to Abraham, "Be not displeased because of the boy and because of your slave woman. Whatever Sarah says to you, do as she tells you, for through Isaac shall your offspring be named. (13) And I will make a nation of the son of the slave woman also, because he is your offspring."

Before we come to Gen 22:2 Ishmael had already departed from Abraham (see Gen 21:20-21). Isaac was Abraham's only son by Sarah, and the only son through whom God's promises to Abraham would be fulfilled.

Gen 21:20-21 ESV And God was with the boy, and he grew up. He lived in the wilderness and became an expert with the bow. (21) He lived in the wilderness of Paran, and his mother took a wife for him from the land of Egypt.

It was through Isaac that "all the nations of the earth be blessed" (through Jesus). Jesus was descended from Isaac not Ishmael (Mat 1:2, Luke 3:34). After God tested Abraham, God again ratifies the covenant between Himself and Abraham.

Gen 22:17-18 ESV I will surely bless you, and I will surely multiply your offspring as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of his enemies, (18) and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice."

The NT also makes clear that Isaac was the heir to the promises of God to Abraham not Ishmael.

Gal 4:30 But what does the Scripture say? "Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman."

Rom 9:6-9 ESV But it is not as though the word of God has failed. For not all who are descended from Israel belong to Israel, (7) and not all are children of Abraham because they are his offspring, but "Through Isaac shall your offspring be named." (8) This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring. (9) For this is what the promise said: "About this time next year I will return and Sarah shall have a son."

Here are John Gill's comments:

"thine only son Isaac; for, though Ishmael was his son, he was a son by his maid, by his concubine, and not by his wife; Isaac was his only legitimate son, his only son by his lawful wife Sarah; the only son of the promise, his only son, in whom his seed was to be called: "

Larry Wilson comments;

Two things stand out in this verse. First, God called Isaac Abraham’s "only son." Why did God say this when Abraham was also Ishmael’s father? Evidently, God called Isaac Abraham’s "only son" because Isaac was the son of Abraham and Sarah. The point is that God viewed Isaac as the one entitled to the posterity and property of his father. Because God had given Abraham three perpetual covenants, Isaac would be the son through whom those promises would be honored. Consequently, God called Isaac Abraham’s "only son."