Sometimes, things are so "obvious" that we don't even stop to think about them. One of the most simple and powerful apologetic tools for a Catholic is the question, Why Sunday?
We all know that Christians must set apart Sunday as a day of worship, the Lord's Day, and always have for nearly 2,000 years. The question is: Why?
First, here is why a skeptic will have no way to explain why Christians worship on a Sunday, the first day of the week.
The Bible teaches that God created the world in six days and rested on the seventh day. This day of rest is Saturday, which has been observed by Jews as their holy day of worship for thousands of years.
Jesus and His early followers were all Jews, hence they held the Sabbath (Saturday) as holy. Jesus was executed on a Friday, leaving His followers apparently defeated. So, what occurred to make this group of Jews suddenly adopt Sunday as their holy day? This is a historical question which frankly has no decent answer aside from the one that a skeptic cannot give: That Jesus Christ rose from the dead on a Sunday morning, the first Easter, proving His divine nature and power over death.
Here is a further exploration of why we need to explain that first Easter-
Another point, which few people know about, is the Quartodeciman controversy. During the second century of Christian history, there was a well documented dispute about whether to celebrate Easter always on a Sunday (the Western practice) or on the specific date of the Lord's resurrection, regardless of what day of the week that fell upon (the Eastern practice at the time). The fact that this dispute arose strongly suggests that there really was a resurrection event on a specific historical date, which was a Sunday!
Protestants, of course, can agree with all that. But they cannot answer this: What would you say if your pastor announced in his sermon that in the future all their services would be conducted on Fridays with no Sunday services? The pastor's announcement satisfies the Biblical command to meet together (Hebrews 10:25). The book of Acts, chapter 20 verse 7, makes mention of St. Paul breaking bread on the first day of the week, but this is merely mentioned as part of a narrative, not a command to all Christians. The pastor explains to the congregation that he has missed too many NFL games in his life and so Friday works better for him. How can a Protestant tell his pastor that it is essential to worship on Sundays when the Bible does not say that?
The Protestant will appeal to "tradition" by saying that Christians have always met on Sundays to commemorate the Lord's resurrection. Here is the contradiction: the Protestant also denies the authority of tradition at the same time.
In a similar vein, the Protestant cannot explain why he must celebrate Christmas at all or specifically on December 25-
Sunday is crucial to who we are as followers of the risen Lord. In the year 304 AD, a group of 49 Christians in North Africa accepted martyrdom rather than giving up the Sunday celebration. They said, "Without Sunday, we cannot live!" Pope Benedict XVI recounts this tale for us, speaking at the Italian National Eucharistic Congress on May 29, 2005-
Christ's Resurrection happened on the first day of the week, which in the Scriptures is the day of the world's creation. For this very reason Sunday was considered by the early Christian community as the day on which the new world began, the one on which, with Christ's victory over death, the new creation began.
As they gathered round the Eucharistic table, the community was taking shape as a new people of God. St Ignatius of Antioch described Christians as "having attained new hope" and presented them as people "who lived in accordance with Sunday" ("iuxta dominicam viventes"). In this perspective, the Bishop of Antioch wondered: "How will we be able to live without him, the One whom the prophets so long awaited?" (Ep. ad Magnesios, 9, 1-2).
"How will we be able to live without him?". In these words of St Ignatius we hear echoing the affirmation of the martyrs of Abitene: "Sine dominico non possumus".
It is this that gives rise to our prayer: that we too, Christians of today, will rediscover an awareness of the crucial importance of the Sunday Celebration and will know how to draw from participation in the Eucharist the necessary dynamism for a new commitment to proclaiming to the world Christ "our peace" (Eph 2: 14). Amen!