I am not a Sabbatarian, and I enjoyed Gary North’s appendix to Rushdoony’s Institutes of Biblical Law on “The Ethics of Sabbath-Keeping”, in which he points out the wide gulf that separates modern Christian Sabbatarian practice from the OT’s much more serious and consistent practice.
The origin of Sabbatarianism is usually traced to Constantine, but an inspection of his decree concerning Sunday reveals something different, and more moderate:
On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed. In the country however persons engaged in agriculture may freely and lawfully continue their pursuits because it often happens that another day is not suitable for grain-sowing or vine planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost.
Agricultural labor was, for the OT sabbath laws, work par excellence. For Constantine to permit it means that his position is not Puritan or Westminsterian Sabbatarianism, but something more like the Heidelberg Catechism’s position: Christians should worship on Sunday, but are not forbidden from doing work.