Besides being one of the 10 Commandments, God also says the seventh-day Sabbath is a sign of the people He has set apart as holy.

In explaining one reason He expected His people to observe the Sabbath, God told Moses : “Speak also to the children of Israel, saying: ‘Surely My Sabbaths you shall keep, for it is a sign between Me and you throughout your generations, that you may know that I am the LORD who sanctifies you’” (Exodus 31:13).

Here we see that the Sabbath is a perpetual covenant. This means that it is going to continue forever.
Reflecting the ongoing existence of the Sabbath
even after Christ returns to this earth, God inspired the prophet Isaiah to write: “‘For as the new heavens and the new earth which I will make shall remain before
Me,’ says the LORD, ‘So shall your descendants and your name remain. And it shall come to pass that from
one New Moon to another, and from one Sabbath to another, all flesh shall come to worship before Me,’ says the LORD” (Isaiah66:22-23).

When Christ came to earth, He observed the seventh-day Sabbath: “So He came to Nazareth, where He had been brought up. And as His custom was, He went into the synagogue on the Sabbath day, and stood up
to read” (Luke 4:16). Jesus Christ’s disciples and the first-century Christians also continued to remember the
Sabbath:
“So when the Jews went out of the synagogue, the Gentiles begged that these words might be preached to them the next Sabbath. Now when the congregation had broken up, many of the Jews and devout proselytes followed Paul and Barnabas, who, speaking with
them, persuaded them to continue in the grace of God. On the next Sabbath almost the whole city came together to hear the word of God" (Acts 13:42-44). “Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where there was a
synagogue of the Jews. Then Paul, as his custom was, went in to them, and for three Sabbaths reasoned with them from the Scriptures, explaining and demonstrating that the Christ had to suffer and rise again from the dead, saying, ‘This Jesus whom I preach to you
is the Christ’” (Acts 17:1-3). “Imitate me, just as I imitate Christ” (1Corinthians 11:1).“He who says he abides in Him ought himself to walk just as He walked” (1 John 2:6).
Through the ages there have always been
people who continued to obey God’s
commandment to keep the seventh day holy,
and this practice continues to identify them
today.
https://lifehopeandtruth.com/bible/10-commandments/sabbath/sabbath-sign/