Yes, the Sabbath is still relevant today. It is a sign between God and His people, intended to be kept throughout generations as a perpetual covenant.
God Himself declared, "Verily My Sabbaths ye shall keep: for it is a sign between Me and you throughout your generations; that ye may know that I am the Lord that doth sanctify you" (Exodus 31:14-17).
The Sabbath is not just for one group of people, but for the world, and it will continue as a sign of God's power as long as heaven and earth endure. Isaiah 66:23 speaks of a time when, in the new earth, people "from one Sabbath to another" shall come "to worship before Me, saith the Lord."
The Sabbath question is presented as a key issue in the final conflict, a test between loyalty to God and the principles of His kingdom, versus allegiance to other principles.