The Catechism in Questions & Answers

321. How do we keep the Sunday holy?

The Sunday should be a day of restand a day of celebration for the soul. Above all, we keep the Sunday holy by worshipping God in divine service, absorbing His word in faith, having our sins forgiven, and partaking worthily of the body and blood of Christ in the sacrament of Holy Communion. Keeping the Sunday holy also entails that we preserve and intensify the effects of the divine service upon us.
Those who cannot attend divine services hallow the Sunday by seeking a connection with God and the congregation in prayer. This applies, for example, to those who have to work, as well as the sick, the disabled, or the aged.
The commandment to keep the Sabbath holy calls upon believers to examine their activities to determine the degree to which these are consistent with the purpose of the day that is dedicated to the Lord.