The seventh-day Sabbath is a perpetual sign of identification, something that anybody familiar with the way we live our lives can observe us doing. God had done that on purpose: He made the Sabbath the sign so that anybody can see it. Anybody who knows us can see that we keep the Sabbath.
On the flip side, the world seems to keep every day except the one that God assigns. He made holy a period of constantly recurring time so that anybody familiar with His children—those who show His characteristics—would be able to observe their example and be witnessed to, without a word having to be said. The Sabbath commandment contains the holy days within its scope.
If we respect, fear, and love God, we will believe what He says and submit to it. What does the world do in regard to this commandment? The world's churches argue against keeping it and resolve not to. They denigrate it as being of no value except as ceremonial and easily replaceable. They apply the commandment as an injunction merely to keep one day in seven—and then do not even keep that one day.
However, they profess Christianity, to follow Christ, just as the Jews professed that their spiritual father was God. In John 8:44, Jesus calls them liars. The world does this despite the fact of the clear witness that God left in His Word that Jesus, by His own admission, said He did not come to destroy the law. He obviously kept the Sabbath Himself, and the apostles (that He instructed for three-and-one-half years) continued to keep it as an example to the church. No command anywhere in the Bible does away with the Sabbath command or any other of the Ten Commandments.