Even a quick reading of Isaiah 56 reveals that, as God is displaying his personal and “familial” nature to the Jew, as well as to the foreigner and eunich, the Sabbath plays a critical role in this chapter. Why? Is it for today? Are we required to obey it?
Succintly, no! Here’s a bit of explanation. The sabbath was strictly a sign for the Jews given to them as part of the Mosaic law. It was never given to the Gentiles, except for here in Isaiah 56. And why here? Because as their return to Jerusalem and Jewish worship was prophesied, God was asking all who were part of his people to return to his commandments as given to his people. This was important when they returned to rebuild the walls and the temple (Nehemiah and Ezra), and it will be important in the New Jerusalem (Millennium an afterwards) when God reigns visibly from the Holy City. At that point, I believe those in the New Jerusalem will once again return to worshipping on the sabbath (partly based on Is. 56). But for now, it is not in play as Jewish worship has not been reinstated during this parenthetical time of the church.
And this makes sense, especially knowing that sabbath means “last day.” Truly, in heaven we will finally be ‘resting’ from all our earthly serving and working and finally able to completely and fully worship God — and only God! What a ‘rest’ that will be, eh? Till then, we find our rest in him. When that day comes, we’ll find our rest with him.