It is a mere assumption that all is mentioned there.
To do so you need to deny a great deal of the New Testament where the New Covenant is layed out and expounded upon
Once again you deny much
If you read the New Testament you see gentiles included
Gal 3:7–9 Therefore, be sure that it is those who are of faith who are sons of Abraham. The Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “All the nations will be blessed in you.” So then those who are of faith are blessed with Abraham, the believer.
Gal 3:26–29 For you are all sons of God through faith in Christ Jesus. For all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Greek, there is neither slave nor free man, there is neither male nor female; for you are all one in Christ Jesus. And if you belong to Christ, then you are Abraham’s descendants, heirs according to promise.
Rom 4:16–17For this reason it is by faith, in order that it may be in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, (as it is written, “A father of many nations have I made you”) in the presence of Him whom he believed, even God, who gives life to the dead and calls into being that which does not exist.
Acts 13:47For so the Lord has commanded us: ‘I have appointed you to be a light for the Gentiles, that you would bring salvation to the end of the earth.’
Acts 28:28Therefore let it be known to you that this salvation of God has been sent to the Gentiles. They also will listen!”
Rom 1:16For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.
Gal 3:8And the scripture, foreseeing that God would justify the Gentiles by faith, proclaimed the good news in advance to Abraham: “In you all the nations will be blessed.”
And will note in Gal 3:8 Paul proclaims the justification of the gentiles based upon God's promise to Abraham that "In you all the nations will be blessed.”
As was stated multiple times in the Old Testament
Gen 17:5“ No longer shall your name be called Abram, But your name shall be Abraham; For I will make you the father of a multitude of nations.
Genesis 18:18 (NASB 95) — 18 since Abraham will surely become a great and mighty nation, and in him all the nations of the earth will be blessed?
Gen 22:18 In your seed all the nations of the earth shall be blessed, because you have obeyed My voice
