The Sabbath Commandment is one of the Ten Commandments!
Yes, it is but, for the Jews only. The Gentiles are also commended (not commanded) to rest for a day in seven but it does not have to be the seventh day of the week. It can be any day they please. If they, after reading Isaiah 56:1-8 decide to join God's Covenant with His People, then, they become liable to keep the Sabbath holy.
Observing the Sabbath is resting on the seventh day of the week. The Sabbath is a day of rest. As God rested on the seventh day, so should we each week.
This is as a Jew. Gentiles can convert or join God's covenant people, in covenant with God according to the covenant God made with the nation of Israel through the prophet Moses at Mount Sinai. I am a convert or a proselyte. Of Israel, of the United States of America, and a Christian. I study Torah, the TaNaKh, the Old Testament, the New Covenant or the Apostle's Writings, the whole Bible. I was a Christian before converting to Judaism and I still am. Is this a righteous proselyte? There has been sin in my life, but as a Christian I already accepted the truth of the whole Bible before studying Torah, the first five books of the Bible, even the Hebrew Bible or the Christian Bible. As a Christian there were still sin issues, that should not have been. As a Jew, there is the Torah and God's commands without wondering about sin, the definition of sin, or what sin is. God's Law tells us what sin is. This is why the Bible says that sin is transgression of the law. We are not to live in sin, but to live righteous lives.
The Sabbath is one of the Ten Commandments. The Ten Commandments are the covenant. And there is more even in Moses or Torah (attributed to Moses or about or from Moses or the time of Moses originating with Moses though Genesis must have been written after Moses and yet the events occurred beforehand).
The new covenant was to be with the house of Israel and the house of Judah, and it came in Yeshua HaMashiach, Jesus the Christ. It is not like the old which the people broke. It is God's law written on hearts and minds. This is either the Law of Moses or something else. But I observe Torah, the Law of Moses, though as a convert or a proselyte and therefore of Israel and practicing Judaism, whether of the tribe of Levi, and we have or there are the Ten Commandments and even the 613 commands of Torah and the 1050 commands of the New Testament, all to be observed or which we are to observe or we are observing or we observe. There are others throughout the Prophets and the Writings. I have never been to Israel.