In Genesis 1—2, God created the universe and everything in it during six days and rested on the seventh day. In Exodus 20, the Israelites were given the Ten Commandments that included, "Remember the Sabbath day, to keep it holy" (verse . To keep it holy involved doing no work on this day.

In the New Testament, Jews continued to keep this Sabbath law. The religious leaders even accused Jesus of working on the Sabbath when He healed a man on a Saturday. After the resurrection of Jesus took place on Sunday, the "first day of the week" in the Jewish calendar, Christians began to gather on this day to worship Christ (Acts 20:7; 1 Corinthians 16:2).

Later in the New Testament, the apostle Paul would have to deal with those who continued to argue that Christians must keep the Jewish laws. When he wrote to the Galatian Christians, he was distressed at their immaturity regarding the observance of special days: "But now that you have come to know God, or rather to be known by God, how can you turn back again to the weak and worthless elementary principles of the world, whose slaves you want to be once more? You observe days and months and seasons and years! I am afraid I may have labored over you in vain" (Galatians 4:9-11).

In Romans 14:5-6 Paul commanded the Roman Christians, "One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind. The one who observes the day, observes it in honor of the Lord." It is clear here that the Saturday Sabbath was not a requirement for Christians. There was nothing wrong with keeping the Sabbath, but it was also no longer a law for Christians.

But has the "Sabbath" changed to Sunday? The Sabbath has always been on Saturday. Some early Jewish Christians observed the Sabbath on Saturday and then gathered with Christian believers to worship on Sunday. Sunday worship became a tradition among Christians very early, but was never demanded as a law. Instead, it was later in church history that some attempted to argue that Sunday was the Sabbath and required rest, church attendance, and that businesses be closed.

Scripture actually teaches that Christians are to gather regularly and worship is to occur at all times. The earliest church in Jerusalem added to their number daily (Acts 2:47). Acts 2:46 records, "And day by day, attending the temple together and breaking bread in their homes, they received their food with glad and generous hearts." It appears they gather several times each week, either as a large group or in homes, to worship Christ and enjoy the encouragement of fellow Christians.

In summary, the Sabbath was a law for the Jewish people, not for Christians. Many Christians have met on Sunday for worship since the earliest times based on when Jesus rose from the dead. Yet Scripture also reveals that the earliest church worshiped much more than once each week. The decision to practice a Sabbath rest, whether on Saturday or Sunday or some other day, is one of personal choice but is not the command of Scripture.
http://www.compellingtruth.org/Saturday-Sunday.html

The Sabbath is the seventh day in the hebrew calender.

Sabbat is the seventh day the last day of the week. Which was commanded to be kept holy.

"Zakhor et yom ha shabbat le kaddesho"

"Remember the day of sabbat for holiness"

Sabbat is the only week days that was single handedly named by God himself. The rest days were called Day 1, Day 2 and so on..

So in the real sense if Sabbat is on the seventh day, then seventh day is the last day of the week(known as Saturday), last day of the week is the weekly sabbath day(day of rest).

Since Sunday is not Saturday then Sunday cant be the true Sabbat day.

Shabbat shalom le makhbir!