Reformed theology holds that the Sabbath commandment is part of the moral law (not merely the Mosaic ceremonial law) and is therefore perpetually binding on Christians. The Westminster Confession (Chapter XXI.7–8) teaches that the fourth commandment requires one day in seven to be kept holy to God; that the Christian Sabbath is the Lord's Day (Sunday), the first day of the week, commemorating the resurrection; and that it is to be spent in public and private worship, works of necessity and mercy, and rest from ordinary worldly activities.

This Sabbatarian view distinguishes Reformed theology from Lutheranism (which treats Sunday worship as adiaphora) and from Seventh-day Adventism (which insists on Saturday). The Westminster Larger Catechism (Q&A 115–121) gives detailed positive and negative requirements for Sabbath observance. The Heidelberg Catechism (Q&A 103) interprets the Sabbath as requiring regular attendance at the assembly of God's people and contributing to works of mercy. While practice varies considerably in contemporary Reformed churches, the Westminster Standards represent the classic confessional position on Sabbatarianism.