Part of what you said above is accurate as shown below.
Then you misunderstood what Isaiah 56 is saying.
If you read the text below from Isaiah 56 this should clarify what you misunderstood.
Isaiah 56:6
Also the foreigners who join themselves to the Lord, to minister to Him, and to love the name of the Lord.
To be His servants, every one who keeps from profaning the sabbath and holds fast My covenant.
Isaiah 56:7
Even those I will bring to My holy mountain and make them joyful in My house of prayer.
Their burnt offerings and their sacrifices will be acceptable on My altar.
The codified law strictly identifies the condition that any Gentile sojourning in Israel must perform. In order
to be a member of that covenant between God and Israel, Exodus 24.
That condition requires the male to be circumcised.
Then that Gentile is like a Jew but is not a Jew and is in covenant to obey the codified law of Exodus 24.
Exodus 12:48-49
But if a stranger sojourns with you, and celebrates the Passover to the Lord, let all his males be circumcised,
and then let him come near to celebrate it; and he shall be like a native of the land. But no uncircumcised person
may eat of it. The same law shall apply to the native as to the stranger who sojourns among you.
A Gentile living outside of Israel is not permitted to join the covenant of Exodus 24.
A Gentile who is uncircumcised and living outside of Israel cannot follow the codified law stated in Exodus 24.
because they are not members of the covenant, they are not legally bound to the codified law.
If you really want to perform the offerings, the sacrifices, the Passover, the Sabbath. Then you you must join
that covenant in Exodus 24.
That's what the text states.
It is interesting how you see this passage in Isaiah, however I see it with a different lens.
"Also,
the foreigners who join themselves to the Lord," meaning a Gentile who back then typically worshiped pagan gods, aligned themselves to the God of Abraham, Isaac, and Jacob, instead of pagan gods. "to minister to Him, and to love the name of the Lord.
To be His servants," meaning the Gentile has a heart for the God of Abraham, Isaac, and Jacob, instead of pagan gods. "everyone who keeps from profaning the sabbath
and holds fast My covenant", meaning if the Gentile not only aligns and has a heart for the God of Abraham, Isaac, and Jacob, instead of pagan gods, but also keeps the covenant of the sabbath that God made with the Jewish people. If you keep reading on it says if they did these things God would bless them.
Isaiah 56:7 is referring to the future, restored Temple in Jerusalem—God’s house—as the place where faithful Gentiles who join themselves to YHWH will be welcomed, accepted, and have their worship received by God.
But the verse is doing far more than describing a building. It is making a
theological declaration about the destiny of the nations, the nature of worship, and the identity of God’s people in the age of restoration. Reading further in that verse it says, "
my house shall be called a house of prayer for all nations". House of Prayer is future tense; therefore, he is
not describing Solomon’s Temple (destroyed in 586 BCE). It is describing the
future restored Temple of the post‑exilic and messianic age. Isaiah 56:3–8 addresses two groups historically excluded: Foreigner and eunuchs, Isaiah 56 overturns these exclusions
in the age of restoration.
Please remember that Isaiah is a prophetic book, so while he was speaking in the present tense about Gentiles joining in to keep the Shabbat, he also added a prophetic inference concerning Gentile standing in the future, ok course by way of Jesus.
You said, "The codified law strictly identifies the condition that any Gentile sojourning in Israel must perform. In order
to be a member of that covenant between God and Israel, Exodus 24." I read this chapter, but it does not say anything about Gentiles getting circumcised that I can see. Please provide the verses, maybe I am missing it.
Now your assessment of Exodus 12:48-49 is correct particularly back then, but the Passover is a different high holy day then the high holy day of Shabbat. The discussion is on the Shabbat, not Passover, correct? I can get into more details about the Passover and Gentiles not being included in this, but this particular thread is discussing the Shabbat. If there is a thread about the Passover, let me know and we can discuss the Passover in that thread if you like. Let me know.
Nevertheless, I appreciate how you are keeping the distinctions between Jews and Gentiles, because these distinctions are important. One law advocates try to remove those distinctions.