Yes, the Sabbath is still very relevant today. It's a sign between God and His people, meant to be kept throughout generations.
God Himself said, "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 importance of the Sabbath will continue as long as heaven and earth exist, as a sign of God's creative power. The Bible says that in the new earth, people will worship God "from one Sabbath to another" (Isaiah 66:23).
The Sabbath is a vital part of God's law and a way to show whether we are loyal to God or following other principles. It is a sign of whose kingdom we belong to.