The third commandment is “Remember to keep holy the Lord's Day.” We may be tempted to think at face value that the keeping of Sunday only means we have to “Go to church!” However, might we open our minds to a much more meaningful approach to living this command that invites a greater love of God and an experiencing of heaven.
The original formulation from Exodus 20:8-10 exhorts to keep holy the “sabbath”: the day of resting from labors that God enjoined upon His people Israel in making a covenant with them. This day was understood in the Old Testament as the seventh of the week (what we know as Saturday) mindful of Genesis 1 when God spoke and created the universe over six days, resting from His labors on the seventh day, setting this day apart as a proper occasion to glorify God and His works. Our Christian practice of keeping Sunday instead of Saturday is rooted in the resurrection of Jesus which took place on a Sunday – as the holy women who first witnessed the empty tomb went out to it “early on the first day of the week,” or on Sunday (see Matthew 28:1, Mark 16:2, Luke 24:1, or John 20:1). Very early in the Church’s life Sunday became the day of worship in connection with this truth of Jesus’ resurrection. Commentaries of the early Church fathers and saints testify to keeping Sunday each week as both a celebrating of the day on which Jesus was raised from the dead and as the ushering in of a new creation (and thus, the concept of the “8th day” that comes after the first week of creation and the sabbath and that the points to the new creation or endless day of eternity in the Trinity).
The Lord’s Day is primarily then a day of renewing the covenant on that day when our salvation was accomplished – as every Sunday is as Easter. The “rest” that is exhorted for Sunday is primarily understood as “restorative” wherein our proper participation in the worship of the Church through the Eucharist is meant as both a celebrating of what Christ accomplished in his Paschal sacrifice and a partaking in the fullness of communion that is yet to be fully revealed in eternity (and not simply to not work for the sake of not working or a going to church just to go). Our rest on Sunday primarily seeks to glorify God and to receive sanctification that renews and strengthens us in our pilgrimage of faith. Rest therefore is rooted in our participation in the Mass. Such rest extends to our being able to put aside the work of the other days of week for deliberate time with family and to carry out works that build up our lives and those of others (remembering Jesus’ own example of healing and doing good on the sabbath, such as in Mark 3:1-6 when He heals on the sabbath).
Practically, this commandment establishes that our keeping holy the Lord’s Day obliges us to participate in Holy Mass on Sunday (or Saturday evening). While we can be excused from this obligation if circumstances beyond our own control prevent us from such worship, might we always keep in the front of our minds the truth of love – that one who loves seeks the good of the other and the one who is loved seeks to return love. God loves us so greatly that he willingly gives His own life (in the Eucharist) to us so that He might dwell within us. Love, then, calls us to offer ourselves in return, giving ourselves to God in true worship (through the humble and complete gift of ourselves to God in the right worship offered in the Mass). Sunday Mass is therefore more than “fulfilling an obligation;” it is a true way of loving, learning to rest in the Lord who gives himself to us and desires our eternal life in his presence – and thus the Eucharist gives us a foretaste of heaven.
For further reading: In the Catechism of the Catholic Church, paragraphs 2168 - 2195 gives teaching the Third Commandment – including fitting perspective on Sunday rest.