Biblical explanation
Paul writes: "One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind." Romans 14:5 The surrounding context is important. Romans 14 begins by discussing disagreements over "doubtful disputations." Romans 14:1. Paul then immediately discusses eating and not eating: "For one believeth that he may eat all things: another, who is weak, eateth herbs." Romans 14:2 Verse 6 continues the connection between the day issue and eating: "He that regardeth the day, regardeth it unto the Lord; and he that eateth, eateth to the Lord." Romans 14:6 Therefore, Romans 14 is dealing with disputed practices among believers rather than explicitly announcing that God has abolished the fourth commandment. Romans 14:5 does say that some believers regarded one day differently from another. It does not specifically identify the seventh-day Sabbath, nor does it explicitly say that the fourth commandment was abolished.
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.