The Sabbath is the seventh day of the week.
In the Torah we learn about the Sabbath. We learn about the six days of creation and we learn that God rested on the seventh day from all that He had created and made.
God commanded us, the people of Israel, to observe the Sabbath each week, the seventh day of the week. For six days we are to do our work. But the seventh day, the Sabbath, is a day of complete rest.
Yup...made for man...not just one tribe of Israel...and not just Israel...non natives too...
And working animals...
His concern was that it be kept and not broken even after He was killed resurrected and returned to heaven...the cross did NOT anull or change or destroy Sabbath keeping...He commanded believers pray that times of troubles would not disrupt its sacredness...He didn't command that prayers be said that the temple be spared...or even Jerusalem...or that lives would be preserved...just that the Sabbath keeping would not be broken...
And Isaiah says from Sabbath to Sabbath all will come to worship again...
Is why Paul writes clearly that a Sabbath keeping...seventh day rest day...remains for the people of God...
And the day starts in the morning.
"When the Jews returned to Palestine after their Babylonian exile (516 B.C.E.) they brought back with them the Babylonian astronomy and way of reckoning time..." (What is a Jew, p. 108).
"In order to fix the beginning and ending of the Sabbath-day and festivals and to determine the precise hour for certain religious observances it becomes necessary to know the exact times of the rising and setting of the sun. According to the strict interpretation of the Mosaic law, every day begins with sunrise and ends with sunset... (Jewish Encyclopedia, p. 591-597).
"Days were reckoned from morning to morning... Following the reign of King Josia (c. 640-609), and especially after the Babylonian exile a number of significant and enduring changes occurred in the Israelite calendar showing that the Jews gradually adopted the Babylonian calendar of the time...the seven day week persisted despite its failure to divide evenly either the month or the year. The day however, was counted from evening to evening, after the Babylonian fashion..."
(New Catholic Encyclopedia -Volume 11, p.1068).
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http://discoveryupdate.com/article10.htm