I acknowledge that Bishop J.C. Ryle regarded Sunday as the Christian Sabbath. Yet, his words are still instructive:

My own firm conviction is, that the observance of a Sabbath Day is part of the eternal law of God. It is not a mere temporary Jewish ordinance. It is not a man-made institution of priestcraft. It is not an unauthorized imposition of the Church. It is one of the everlasting rules which God has revealed for the guidance of all mankind. It is a rule that many nations without the Bible have lost sight of, and buried, like other rules, under the rubbish of superstition and heathenism. But it was a rule intended to be binding on all the children of Adam.

Ryle, J.C. Knots Untied, 1877.