The Catholic Church admits to changing the day of worship from Sabbath to Sunday. Protestants who keep Sunday are bowing to presumed Catholic authority.
Whether a matter is salvational is the wrong question. There is a better question and another approach to evaluating matters that will put us on better footing.
John Ritenbaugh, reflecting on the propensity of people to break the Sabbath, explains that the carnal mind is enmity against God. Human nature is hopelessly perverse. In a book review of Steven Miller's book The Peculiar Life of Sundays, appearing in the Charlotte Observer, the reviewer suggests that even the worldly 'Sunday …
Catholics and Protestants, because of lack of belief, do not find the Bible a sufficient guide to salvation. They claim to believe Christ, yet disobey.
God has sanctified no day other than the Sabbath. Sunday worship is a pagan deviation, perpetuated by Gnosticism, a movement that despises God's laws.
The days, months, and times of Galatians 4:10 do not refer to God's Holy Days (which are not weak or beggarly), but to pagan rites the Galatians came out of.
The phrase 'first day of the week' is used 8 times in scripture, but none does away with the Sabbath nor establishes Sunday as the 'Lords Day.'
God gave the Sabbath to His people so they can know Him intimately. Idolatry, scattering, and captivity are the natural consequences of Sabbath-breaking.
The elect are not immune to antinomian deception, including the doctrine of eternal security, the total depravity of man, unconditional love, and cheap grace.
Hosea is an account of Israel's unfaithfulness to the covenant with God, and the redemptive work of God to rescue His unfaithful spouse from slavery.
God gives conditions for acceptable sacrifices and offerings, differentiating the holy and authentic from the defiled, unclean and strange.