Biblical explanation
The resurrection took place on the first day of the week. This gives Sunday an important place in Christian history. The New Testament also records first-day gatherings, such as Acts 20:7. However, there is an important distinction between recording an event and commanding an institution. The Bible records: Jesus' resurrection on the first day A gathering in Troas on the first day Instructions concerning collections on the first day But Scripture never says: "Keep the first day holy." By contrast, the fourth commandment explicitly says: "The seventh day is the sabbath of the LORD thy God." Exodus 20:10 Sunday worship has a long Christian history, but the question of which day Scripture commands should be answered from the biblical text rather than from later tradition.
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.