Romans 14:5-6a (NKJV) 5 One person esteems one day above another; another esteems every day alike. Let each be fully convinced in his own mind. 6a He who observes the day, observes it to the Lord; and he who does not observe the day, to the Lord he does not observe it.
Again, not a reference to the 7th day Sabbath. There many “holy days” back then. Is Christmas a holy day? It’s not in the Bible but many treat it as the “holiest time” of the year. Romans was wrote by the Apostle Paul, a great believer in the Law (Ten Commandments).
Exactly what is meant by resting in Christ, with His Righteousness imputed to the true believer.