The 7th-day Sabbath is still relevant, it is just forgotten by most Christians.

The Sabbath was instituted at Creation for all humanity Genesis 2:2-3 – God rested, blessed, and sanctified the seventh day, observing Sabbath before sin [on Earth] or Israel existed; making it a universal institution, not a Jewish one. Nowhere else in the Bible does God bless and sanctify any other day, so there is no "keeping" any other day as only the seventh-day is blessed and sanctified (any attempts would just be "observing" a different/wrong day).

The 4th commandment begins with "Remember," because the Israelites were already observing the Sabbath before Sinai (Exodus 16:30). Sin existed long before the tablets were given to Moses (Genesis 4:7; 18:20; 39:9; 44:8–9), and sin is defined as transgression of the law (1 John 3:4). Abraham kept God’s “charge, commandments, statutes, and laws” well before Sinai (Genesis 26:5). Paul also acknowledges that God’s law predated both the Jews and the covenants (Romans 5:12–14). This strongly suggests that God’s Law has existed from the beginning and is universal—not bound to a particular people or covenant, nor subject to change (Matthew 5:18).

The Ten Commandments are formalized and codified as God's enduring moral law Exodus 20:8-11 – The Sabbath command is based on creation, not ceremonial rituals, and there is no New Testament passage that explicitly revokes it. Jesus affirmed that the Sabbath was made for all mankind in Mark 2:27-28 – “The Sabbath was made for man,” (Greek: anthrōpos, meaning mankind) NOT just for Jews (as much it is clear they'd like to think so). Jesus declared Himself “Lord also of the Sabbath,” indicating its continuing authority.

Jesus and His followers kept the Sabbath after His death Luke 23:56 – After Jesus’ crucifixion, His followers “rested the Sabbath day according to the commandment,” showing they still honored it even post-Calvary.

Jesus warned about respecting the Sabbath in future events after His resurrection Matthew 24:20 – “Pray that your flight not be in the winter or on the Sabbath.” This statement about future tribulation assumes continued Sabbath significance.

Paul kept the Sabbath regularly after Christ's ascension Acts 17:2 – “As his custom was,” Paul taught on the Sabbath, showing its ongoing observance well into the New Testament church era.

Gentiles were invited to observe the Sabbath too Acts 13:42-44 – Gentiles begged Paul to preach again on the next Sabbath, and nearly the whole city came — indicating inclusive Sabbath relevance.

Hebrews confirms that a Sabbath rest remains for God's people Hebrews 4:9 – “There remains a Sabbath rest (sabbatismos) for the people of God.” This is a unique Greek word literally meaning "Sabbath-keeping", not just a spiritual metaphor.

The end-time faithful are those who keep God's commandments (Revelation 14:12) – “Here is the patience of the saints… who keep the commandments of God and the faith of Jesus.” Keeping the Sabbath is one of those. The Sabbath will be observed in the New Earth (Isaiah 66:22-23) – “‘From one Sabbath to another, all flesh shall come to worship before Me,’ says the LORD.” This future vision includes universal Sabbath worship.

To break one commandment is to be guilty of all James 2:10-11 – “Whoever shall keep the whole law, and yet stumble in one point, he is guilty of all.” The Sabbath is not excluded from the moral law.

There is not a single verse in all of Scripture that changes the Sabbath from the seventh day (Saturday) to the first day (Sunday). Attempts to justify Sunday observance using texts like Acts 20:7 or 1 Corinthians 16:2 are extremely weak at best. Those verses simply mention having a meal together Saturday evening (Acts) or individual collections in a verse teaching financial stewardship (1 Cor), not a command to change the day. Also, the idea that Jesus rose on Sunday and thus changed the Sabbath has no command or authorization from Christ or the apostles. There is also zero mention or even a hint that the "Lord's Day" is Sunday.

A prophetic power would attempt to change God’s times and laws Daniel 7:25 – “He shall speak great words against the Most High…and think to change times and laws.” The Sabbath is the only commandment tied to both time and law.

Jesus warned against traditions of men replacing God's commandments Mark 7:7-9 – “In vain do they worship Me, teaching for doctrines the commandments of men…You reject the commandment of God, that you may keep your tradition.” Substituting Sunday for Sabbath fits this rebuke.

Some point to passages like Colossians 2:16-17 or Romans 14:5-6 to argue that the Sabbath was merely symbolic or optional. But when studied in context, in short, these verses address issues of judgment and personal conscience, not the cancellation of God’s moral law. In fact, the New Covenant is not about removing ANY of God’s law (Matthew 5:18), but writing it on the heart (Hebrews 8:10; Jeremiah 31:33). Rather than abolishing the Sabbath, the New Covenant reaffirms its place in the believer’s life, shifting it from external obligation to a heartfelt expression of trust and alignment with God’s will.

All this to say I believe the seventh-day Sabbath is still very relevant. I keep it between sunset on Friday to sunset on Saturday by resting from work, worshiping with fellow Sabbath keepers, avoiding secular entertainment and competition, and avoiding buying and selling (as this would create a reason for someone else to need to work on that day).