Biblical explanation
The Sabbath existed before there was a Jewish nation. Genesis 2 places its origin at creation. Isaiah also presents Sabbath observance in connection with future worship: "And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me." Isaiah 66:23 Revelation's final call to worship "him that made heaven, and earth, and the sea" points back to the language of the fourth commandment. Revelation 14:7; Exodus 20:11. The Bible does not say that the Sabbath became irrelevant after Christ's resurrection.
Key takeaway
Salvation is entirely by grace through faith in Christ. His atoning sacrifice, heavenly ministry, and intercession are the foundation of assurance; obedience, Sabbath faithfulness, and loving service are the fruit of a redeemed life, never a way to purchase acceptance with God.