With all of the calendar changes, wars, natural disasters, and other events, we don't know what day "the seventh day" really is.  We are free to observe whatever day we want.

 

The Response

Consider the Lord's commandment:

Remember the sabbath day, to keep it holy. Six days you shall labor and do all your work, but the seventh day is a sabbath of the LORD your God; in it you shall not do any work, you or your son or your daughter, your male or your female servant or your cattle or your sojourner who stays with you. For in six days the LORD made the heavens and the earth, the sea and all that is in them, and rested on the seventh day; therefore the LORD blessed the sabbath day and made it holy. (Exodus 20:8-11)

 

From this passage we learn two things:

  1. The Sabbath is the seventh day (not a seventh day).
  2. This day is tied to the seventh day of Creation on which God ceased from His work of creating.

This is a specific day tied to a specific Creation event.

Creation to the Exodus

Even if the knowledge of the seventh day was lost at some point after the Creation, God made certain that the people of the Exodus knew exactly what day the seventh day was.  For forty years God provided manna every day (Exodus 16:35), with a double portion on the sixth day (Friday- Exodus 16:5), and none on the seventh day (Saturday- Exodus 16:26-27). 
Israel knew what day the Sabbath was because of the miracle of the manna from heaven.

Post-Exodus Israel

Is it possible that, due to the wars, apostasy, and the Assyrian and Babylonian captivities that the seventh day was lost after the time Israel entered their Land and the manna stopped? Yes, however, this is not borne out by history.  The Jewish nation would have been extremely concerned if the date had been lost because the violation of the Sabbath required the death penalty (Exodus 31:14, 15, 35:2). 
There is no question in ancient Jewish literature about the date of the Sabbath being lost.

The First Century

Even if the date had been lost, when know Christ confirmed the correct date.  Throughout His life, Jesus observed the same Sabbath day as the rest of the Jewish nation, teaching in the synagogues (Mark 1:21, 6:2, Luke 6:6, etc) and performing miraculous healing (Matthew 4:23, 9:35, Luke 13:14, etc).  If Jesus was observing the wrong day then He violated the commandment regarding the Sabbath and He sinned... yet Scripture declares He did not sin (Hebrews 4:15).  Jesus also declared Himself the "Lord of the Sabbath" (Matthew 12:8, Luke 6:5).  He would have been a pretty poor Lord if He didn't even know which day was His. 
Jesus affirmed the Sabbath day recognized by the Jewish people as the correct day.

The Gregorian Calendar

In 1582, the Julian calendar (named after the Roman emperor Julius Caesar) was discovered to be ten days late compared to the expected position of the sun.  It takes the Earth 365 days, 6 hours, and 11 minutes to orbit the sun.  The Julian calendar had not accounted for those additional 11 minutes each year for almost 1,600 years so the date was off by 10 days.  To correct the issue, Pope Gregory instituted what became known as the Gregorian calendar, and added the ten days back.  Adding those ten days changed the number of the date not the day of the week.  In October 1582 when the change occurred, Friday the 5th became Friday the 15th... but it was still Friday.  And the next day was still the Sabbath. 
The Gregorian calendar date change did not change the day of the week.

Today

What about other events and challenges since the first century?  Do we still have the right "seventh day"?  Yes.  And to follow the standard of Scripture (Deuteronomy 19:15, Matthew 18:16, 2 Corinthians 13:1), we must have two witnesses to confirm it.

First, the Jewish people have, for the past two centuries, ceased from their labor every seven days without fail.  In every nation where they have been scattered, Israel continues to honor and celebrate the seventh day as the Sabbath.  There is no question in the minds of millions of Jews over the past 2,000 years which day is the Sabbath.  It has remained consistent with the date Messiah kept.

Second, the Catholic Church also has, for the past 2,000 years honored the first day of the week (Sunday) as the day of the Lord's resurrection.  In every nation where they have gone, Catholics continue to honor and celebrate the first day immediately after the seventh day of the week.  While we aren't Catholics, we recognize the fact that there were no Methodists, Lutherans, or other Protestant denominations that date back to the first century and the time of Christ.  Their observance of the first day affirms the seventh day that precedes it.

The two witnesses to the seventh day Sabbath are the Jewish people (who honor that day) and the Catholic Church (who honors the day immediately after).

 

Jesus declared "A disciple is not above his teacher, nor a slave above his master. It is enough for the disciple that he become like his teacher, and the slave like his master."  (Matthew 10:24-25)  We have not lost the knowledge of the seventh day Sabbath since the time of Christ and we would do well to follow His example.  As He also proclaimed, "If you love Me, you will keep My commandments." (John 14:15)

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