Josh the OP has misunderstood the whole concept of the Sabbath and God's rest. The Sabbath and entering into God's rest are two entirely different subjects.
Originally the Sabbath day was inaugurated by God as the fourth of the Ten Commandments. There is argument whether they are relevant anymore. Some say no as they are all fulfilled in Christ. Some say yes except the fourth commandment and some say yes all are still relevant.
If they are fulfilled in Christ that means we have to live a life that fulfils the law and more so we are set a higher standard.
If they are relevant except the fourth, you have to find scripture that says this and you can’t.
If you believe they are all still relevant you have to work out how to apply them as a promise rather than a command.
The word ‘Sabbath’ as in the Sabbath day appears 60 times in the New Testament (NT). It is the same Greek word in every reference and means a day of repose from secular activity. There is not one case of meaning us entering a permanent Sabbath rest.
This means that the Sabbath Day in the NT is a day, not a permanent fixture.
As far as Hebrews is concerned, we are not talking about a Sabbath day but a Sabbath rest which every believer enters into. In Hebrews 4:9 it says….So, then, there remains a Sabbath rest to the people of God. This Sabbath rest in Greek is a repose of Christianity and it is something that we enter into.
You don’t enter into a Sabbath Day. You observe it.
The previous chapter of Hebrews explains this rest using Moses and the children of Israel as an example. They spent 40 years in the wilderness and as a result did not enter into God’s rest in the Promised Land because of their unbelief.
Belief or unbelief will not and does not make any difference to the keeping of the Sabbath (seventh) day so it is obvious that Hebrews does not refer to the Sabbath (seventh) day.
In Hebrews 4:1 it says….Therefore, let us fear lest perhaps a promise having been left to enter into His rest, any of you may seem to come short.
The Hebrews rest was a promise, not a command and it talks about coming short of it as the Children of Israel did. One does not come short of a Sabbath day because there is no mention anywhere in scripture of coming short of a Sabbath day.
A believer can fall short of entering into God’s rest by continuing in their own works, not by meeting on Sunday. When you do not acknowledge his Lordship in your life and allow him to be Lord of all, you do not enter into rest. That means whether you meet on Saturday or Sunday, you are striving to please God (or your church or church leadership).
And just to throw a spanner in the works, the New Testament Church met every day, not one day a week.