Thank you for the wonderful question. Though it is a very technical question, I hope the choice of date does not prevent any of us from loving Jesus and His people any less.
I gave a sermon about this yesterday, so let me point you there. I spoke briefly on the topic of why Christians worship on the first day, so please take a look: https://www.ljl.church/sermons?i=29
To say briefly, the legal rule from the Ten Commandments to keep the seventh day as Sabbath has not changed. What Jesus teaches is that the Sabbath should be every day.
Today, many people are heavily stressed due to non-rest. I wonder if it was any different during Jesus' day. Jesus came to give us rest—rest in Him.
Jesus affirmed that the Sabbath was not made so people would keep it but for people (to rest!). Jesus declared Himself the Lord of the Sabbath when He saw that the people were instead taxed than able to rest (Matthew 12:1-8). In other words, there is a law to be kept, but Jesus opposed how we changed God's intent to make it harder for us to draw near Him.
We find in the New Testament Jesus basically says all laws are to be kept, but He narrows down the intent to two things: to love God and others (Matthew 22:34-40). How can we do that? To not focus on just keeping the laws, but to do it from the heart?
I teach seminarians and others that Jesus now demands our lives (Romans 12:1) instead of the 10% offerings (tithes). Is that possible to do today? In human thinking, absolutely not! Yet, God enables us (Ezekiel 36:26-27). The crux of the Gospel is that it is not human power or wisdom but God who enables us to keep the perfect law. When we miss the law, God's grace is available to cover us (Romans 5:20).
Now, let me address your question. Why do Christians worship on the first day? Christians worship on the first day because they rest in the finished work of Jesus.
When God created the world, He did in six days. After He was done, He rested (Genesis 2:2-3). This same model was given to the people of Israel. Yet, we must remember the result of sin in Genesis 3:17. Results were easy to produce before the fall. It seemed all nature and living things (plants and animals) worked together to produce the results easily (consider Genesis 2:19-20)! Yet, our toils are not easy, and it does not bring the fruit we often desire.
In Romans 1-3 (and future chapters), the Apostle Paul goes vehemently about how the law cannot be kept. He says the law shows us how sinful we are (Romans 3:20). He also says grudgingly (forcefully) keeping the law does not make us right with God, but a change of heart as a result of the law does (Romans 2:29).
Then, the Sabbath law that God allowed the people of Israel to follow was to show that they could not keep the heart law as originally intended. The people of Israel were to toil and work hard for six days, then rest. Were most people able to rest? You see, God did a perfect job, so He can breathe and say, "It is done. Let's rest!" For us humans, our work is not really complete and satisfactory. So, can we say we can rest as God can rest? Remember, the ability of the people of Israel to keep the perfect commandment was dependent on their salvation! (Consider how the majority of Israel could not get into the promised land and the stories in the books of Judges and Kings).
Now, Jesus' death and atonement completed the heavy burden we had. John 3:16, our familiar verse, confirms that believing in His finished work is sufficient! It is not our works that save us anymore (our works never really measured up anyway, Ephesians 2:1-10)! That is the reason Christians celebrate the rest on the first day, which we call the "Lord's Day."
To be clear, let me summarize what happened. The Jewish people had to rest AFTER their finished work on the seventh day. Instead, Christians rest on the first day, celebrating what Jesus has done. They rest instead of working first so they can cheerfully work throughout the week, knowing that God has provided for all their needs. Instead of working to meet some standard, Christians recognize that all their needs are met and work out of that joy.
Another piece I need to include before I complete this topic is that Jesus calls us to Sabbath every day. The familiar verse is Matthew 11:28-30, where Jesus invites us all to rest in Him, and that is any time. Hebrews 4 talks about the eternal rest that God has prepared for us. The call is for us to believe in Him today (Hebrews 4:7). Today means now, and that time continues. We find Jesus slipping away from the crowd during the day (Luke 5:15-16) and beginning His mornings with God (Mark 1:35). He did not wait until the seventh day to rest; instead, it was His lifestyle to rest in God. We are called to do the same.
And so, I want to affirm I love the Jewish and Seventh-Day Adventist brothers and sisters. I have a friend who is an SDA pastor. We will have to journey on our own to resolve the conflicts in our beliefs, but the Sabbath is not one of them. In the first churches, people gathered daily (Acts 2:42-47 and many others). Christians worship on the first day because of our faith in what Jesus has done, but doing that on Saturday is just as fine. Let us not let the law ever detract us from the first intended commandment, to love.
Des Moines, IA
