Hebrews 8
8 For finding fault with them, he saith, Behold, the days come, saith the Lord,
when I will make a new covenant with the house of Israel and with the house of Judah:
9 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord.
10 For
this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people:
This is specific to say that this applies to the house of Israel and the house of Judah. God even says their fathers were the people God led out of Egypt, so I'd say this is fairly plain language.
Hebrews 10:16
15 Whereof the Holy Ghost also is a witness to us: for after that he had said before,
16 This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;
17 And their sins and iniquities will I remember no more.
18 Now where remission of these is, there is no more offering for sin.
This is quoting and summarizing from
Jeremiah 31
31 Behold, the days come, saith the Lord, that I will make a new covenant with the house of Israel, and with the house of Judah:
32 Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the Lord:
33 But this shall be the covenant that I will make with the house of Israel; After those days, saith the Lord, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people.
And again this is plainly speaking about Israel and Judah.
In Hebrews where this is quoted, notice, "for after that he had said before", this is to say He is referenced what He said through Jeremiah, and there is no change or extending to others. The point of the passage it to affirm the end of sacrifices, that is, the sin offering. But there is no "writing the Law on the hearts of the gentiles" here, at least, not that I can see.
OK, I'm running out of time . . . maybe you will come across my other post, I covered all the verses if I remember right.
Much love!