Why does the Church command us to keep Sunday as the Lord's day?

The Church commands us to keep Sunday as the Lord's day, because on Sunday Christ rose from the dead, and on Sunday the Holy Ghost descended upon the apostles.

     What are we commanded by the third commandment?

By the third commandment we are commanded to worship God in a special manner on Sunday, the Lord's day.

Keep you my sabbath; for it is holy unto you.  (Exodus 31:14)

     How does the Church command us to worship God on Sunday?

The Church commands us to worship God on Sunday by assisting at the Holy Sacrifice of the Mass.

     What is forbidden by the third commandment of God?

By the third commandment of God all unnecessary servile work on Sunday is forbidden.

Six days shall you do work; in the seventh day is the sabbath, the rest holy to the Lord.  (Exodus 31:15)

     What is servile work?

Servile work is that which requires labor of body rather than of mind.

     When is servile work allowed on Sunday?

Servile work is allowed on Sunday when the honor of God, our own need, or that of our neighbor requires it.