Q. Is going to Mass on Sunday part of God’s law or just Church law? Isn’t it possible to “keep the Sabbath holy” in other ways?
A. The term ‘Church law’ gets misused a lot. Something like not eating meat on Friday is a Church law. How we observe the Sabbath is not. That is Divine law because Christ entrusted the Church to the apostles (bishops) who are the teaching authority of Christ; they are given the task to interpret God’s law to help lead us to salvation.
Observing the Sabbath is not a matter of personal opinion or a very subjective idea of ‘I determine what is the Sabbath rest’. When Moses gave this law to the people, he also went on later in Exodus and Leviticus to explain how the Sabbath was to be observed. This included no work and further distinctions on what was work, etc. It is important to note that the people as a community adhered to the same Sabbath observance; everyone observed it in the same way, not as each saw best.
Later, we learn in Acts that on the Day of the Lord (Sunday), the new Christians observed the Sabbath by coming together as a community to celebrate the breaking of the bread and reading of the Scriptures. St. Paul describes these first Masses as partaking of the Eucharist, the singing of psalms, canticles and spiritual songs, teachings from the apostles, collection for the poor, etc. Each Christian did not decide how he would observe the Sabbath; he joined his or her community to observe it together in unity with one other.
We know by the year 130 or so, when St. Justin Martyr gives us a description of the Eucharist (very similar to how we celebrate today), that this was how the expanding church in various regions of the ancient world observed the Sabbath. It was not something imposed by the Church leadership, but how the community joined together to worship God, collect money and food for the poor, visit the imprisoned, and spend the day in prayer and worship of God with family and friends.
So it stands today. We continue what began on the slopes of Mt. Sinai 4000 years ago, gathering as a community of faith to offer God worship and be refreshed in mind and spirit. Honestly, it has only been in the past 50 or so years that people have begun to say that Sabbath observance outside of Mass is somehow acceptable!