Hi Dr. Wendy,
Well, if you are a 7th Day Christian or a Jew you keep it because this Day is Commanded by God. Now with Grace and the Spirit of righteousness in us we will keep it in the Spirit of the Law, Romans 8:1-4
We know that Jesus Christ kept it and taught that none of his Commandments where done away with including the 4th Commandment, Matth ew 5:17-18, Luke 4:16.
. King David said all of God's Commandments are righteousness, Psalm 119:172. The Holy Spirit will write them on our hearts now for those willing to keep them now or later after Christ returns, if you will then keep it Holy, Hebrews 10:15-17, Jeremiah 31:31-34, Ezekiel 36:22-30.
Sunday was not a weekly day of worship until the 2nd century
Sunday is worshipped a a gift to pagans by the Catholic Church to follow them. Protestant churches keep Sunday because they understand it is a gift from the Roman Catholic Church. Martin Luther kept Sunday because he was a Catholic.
Sunday was usually an annual day of worship once a year around Christmas time, but in 135 A.D., Emperor Hadrian of Rome started to keep it as a day of worship once a week dedicated to the pagan sun god, Mithra, to replace the 7th Day Sabbath. He banded Jews and including 7th Day Christians from Rome and forbade them to keep he 7th Day..
Later in the 4th century Constantine made Sunday the official Day for Christianity in Rome. This is where Sunday as a "Christian" day got its start.
Jesus Christ never changed this Day, Hebrews 13:8, which still pictures the coming Millenium as a Day of rest with God, Genesis 2:2-3.and is encouraged by the Holy Spirit to be kept in Hebrews 4:4-12. Remember God said to keep it Holy, Exodus 20:8-11. You will be blessed if you keep it.
It will be finally restored in the Millenium again when Jesus returns, Isaiah 66:22-23, Leviticus 23, as statutes forever.
In the OT the nation of Israel was punished for not keeping it but when they are redeemed they to will keep it, Romans 11:26..
For many centuries God's people kept the Sabbath and were persecute because the world in general would not keep it. It preferred man's pagan days. After Christ comes everyone will have to keep it because any other Day will not be tolerated By God. Then we will have peace on earth, Malachi 3:6 because God still wants us to keep the Sabbath Day Holy, Revelation 22:10-15. It's all a matter of which reward you want!