Armstrongism teaches that the weekly Sabbath—Saturday from Friday sunset to Saturday sunset—is a binding obligation for all Christians. This is not merely a suggestion or optional practice but a central commandment that continues into the New Testament church era. Sunday worship is presented as a pagan corruption introduced by post-apostolic Christendom and has no biblical foundation.

The Sabbath is a sign of the covenant between God and His people and a foretaste of the Millennium. By observing the Sabbath, believers testify to God's creative and redemptive power and maintain allegiance to His law rather than human tradition. The seven annual feast days are equally binding. This emphasis on Sabbath observance is one of the most distinctive and recognizable practices of Armstrongism.