Ok, first of all, Ishamel is still Abraham's son, and he is his first born son whether born from a slave or not. For your information, in those old days, if a son or a daughter is born from a slave, that son or daughter are entitled to the same rights as a son or daughter born to a regular wife. This is confirmed through what has been discovered in Iraq ( Which is where Abraham came from and also, if studied carefully, it shows that Abraham didn't really lie when he said that Sara was his sister, this can be verified but it's a different subject ).
Now, Ishmael is his first born son, and when GOD ask Abraham to take his only son, he means Ishmael not Isaac because Ishmael is about 13 years older than Isaac. I am not bringing this from home, it is written there. The word Ishmael was removed and Isaac was inserted. Please notice the phrase your only son .
Now if we go back to the covenant thing, I can only ask you to read it again and look for the order in which GOD spoke to Abraham. GOD said that he will establish his covenant with Abraham's descendents and that is Ishmael and the upcoming Isaac
Ishmael would be a great nation also. How do we define a great nation according to how YHWH see it. YHWH would only think you are great if you are a worshiper of him. YHWH doesn't care about how strong you are or how fuitfull your nation will be. When YHWH say a nation will be great it can only mean something great will be in that nation.
Now if we go and look at the phrase an overlasting convenant, this can only mean that GOD will make an unbreakable covenant with Isaac and his descendents. If we agree to this fact, then we are removing the idea that YHWH will establish a new covenant with the Gentiles (New Testament) because Paul simply cancelled the convenant of mount Sinai and abolished the use of law.
There is a mistake in Genesis tha can not be denied. I advise you to read through Genesis 22-2 again and see what I mean about your only son.
I am not bringing this garbage from no where. I am bringing this stuff from Genesis.
Very funny how the phrase great nation is ignored, very funny how the phrase your only son is ignored, and very funny how you rely on the phrase overlasting covenant when this actually demolish the idea of a new covenant.
People live in denial I understand, but people can't be this ignorant about the fact that Ishamel was born before Isaac and when YHWH ask Abraham to take his only son he means Ishamel because Isaac wasn't even born at that time.