1. It is reasonable to assume that Jesus kept the Sabbath and therefore the ancient Hebrew calendar and it's Sabbaths, new moons and annual feasts must have been common knowledge at this time.
2. After the sacking of Jerusalem in 70 AD the Jews no longer had a temple to sacrifice in nor a priesthood to do it as they had all been killed. The Romans virtually killed everyone in Jerusalem and Massada where the rest of the rebels ran to. This left the Jewish population decimated and of the Jews living else where in Israel who had survived, by cow-towing to the Romans, very few return or decided to live in Jerusalem after 70 AD. The Sanhedrin however did mange to largely survive and formed a seat of rabbinic learning in the south of Galilee, where they maintained the practice of keeping the ancient Hebrew calendar and it's Sabbaths, new moons and annual feasts by travelling to Jerusalem each month to sight the new moon.
3. Over the successive generations from 70 AD onwards these traumatic events had forced the Jews to look for sanctuary within the rest of the Roman Empire and beyond in what was called the Diaspora. They were refugees scattered in small groups and families, struggling to survive in foreign countries where they were more often than not treated as the lowest of the low.
4. Then after the Simon Bar Kokbha revolt between 132 - 135 AD and Emperor Hadrian's violent response which was one of Rome's largest ever military responses to rebellion in the empire with some 13 legions being sent, (only 4 were sent in 70 AD for example); Hadrian then banned all Jews from even being with in eye sight of Jerusalem by pain of death and after this there were even fewer Jews living in Israel. This also meant the Sanhedrin could no longer visually sight the new moon from Jerusalem in order to know when their Sabbaths, new moons and annual feasts were. Even though the new moon could be sighted from Jerusalem up to 135 AD this meant nothing to the poor survivors living abroad as there was no way that the monthly sightings could be sent to them quickly enough for them to calculate when the Sabbaths, new moons and annual feasts were meant to be. They could try to sight the new moon from wherever they were but then this would be on different days compared to Jews who were living further to the east or west.
5. Instead the Jews found themselves living in an empire which was being taken over by the new Roman Julian calendar, named after Julius Caesar. This new calendar that first took effect in the province of Rome had started on 1st January 45 BC and this day was named 'Friday' (each the 7 days of this new calendar was given a new name, named after a Roman god). However the day before 1st January 45 BC the Romans calculated dates using a completely different ancient Roman calendar that had an 8 day week, where the days were simply named A,B,C,D,E,F,G & H (8 days) and which had been used for hundreds years by the Romans in the province of Rome. The new Julian calendar 7 day week was created by Sosigenes the Greek Mathematician and it had nothing to do with the ancient Hebrew calendar week, as they were totally separate from each other. It then took about 400 years before all the other countries within the Roman Empire were eventually forced to use the new Julian calendar as recorded in history.
6. As the new Roman Julian 7 day week that began separately from the ancient Hebrew week began to take over the Roman Empire, the early church, which was mainly made up of non-Jews (after Peter the first Pope), simply used the new Julian calendar's 7th day (Saturday) as the Sabbath, even though it had nothing to do with the ancient Hebrew calendar and its reckoning of when the Sabbath was. The Roman Catholic church carried on with this regardless of the fact that the Julian calendar was totally different from the ancient Hebrew calendar.
7. From 135 AD to 321 AD over half a dozen generations came and went, with each generation of impoverished Jews continuing the struggle to survive within the Roman Empire. As each generation lived and worked in these countries that were using the new 7 day Julian week, it meant that more and more Jews were forced to work on their Sabbath as calculated by the ancient Hebrew calendar or face becoming even more impoverished. While they tried to maintain as much of their traditions as possible most could not keep their Sabbaths, new moons or annual feasts on the correct day as calculated by their ancient Hebrew calendar. As said even if they tried to sight the new moon from wherever they were living this would not be on the same day compared to Jews who were living further to the east or west, and more importantly on the day the new moon would be seen from Jerusalem. As each generation gradually came and went it became harder and harder to NOT fit in with the new Roman Julian 7 day working week and its Saturday Sabbath. Eventually over these generations the ancient reckoning of the Sabbath as calculated by the ancient Hebrew calendar was practically lost to history and the Jews living in the Empire gradually accepted Saturday as the Sabbath more and more.
8. Then in 321 AD the Roman Emperor Constantine who hated the Jews (along with most of the rest of the Roman world) changed the day of rest on the new Julian calendar from Saturday to Sunday, this forced the impoverished Jews to either work on what many thought by now was the Sabbath (Saturday) or become even more impoverished. This caused and has since caused even more confusion amongst Christians and Jews as to when the real Sabbath is, as really it has never been on Saturday or Sunday on the Roman Julian calendar but has always been calculated by the ancient Hebrew calendar.
9. In response to all this in 359 AD Sanhedrin Rabbi Hillel II in Israel created the new modern Jewish calendar which uses the mathematically calculated Metonic 19 year lunar cycle, that allowed Jews to celebrate all of their new moon days and annual feast days on the same day no matter where in the world they lived (even though half of the time it is a day out compared to the visually sighted new moon from Jerusalem). However, although this gives a good approximation of when the Jewish new moon days and annual feast are, Hillel appears to have not attempted to try and get the Jews to also follow the original Sabbath as calculated by the ancient Hebrew calendar. The reason for this was because the Jews who were scattered across the Roman Empire and beyond were still simply struggling to survive and had become so used to the new Julian calendar and it's Saturday Sabbath, that if they would have tried to go back to worshipping on the correct day as reckoned by their ancient Hebrew calendar it would have placed a further burden on them and put them at risk of being even more persecuted, because taking days off work that were calculated by the ancient Hebrew calendar rather than fitting in with the Julian Saturday Sabbath would have caused confusion and more resentment towards them.
10. The Hebrew calendar and it reckoning of when the Sabbath really was drifted from human history to be almost forgotten. This calendar that was once common knowledge to the ancient Hebrews and the authors of the Bible never thought it necessary to explain this calendar in one convenient place as they never envisaged a time when it would not be used. However, hidden amongst the scriptures of the Bible are many references to the ancient Hebrew calendar and its Sabbaths, new moons and annual feasts, which can be sifted out and reconstructed. This is not an easy thing to do however, if it was then more people would know about it but then most people don't even know about all the above information either, so it is understandable if you have never heard about where and how these snippets of scripture explain the ancient Hebrew calendar. Their are various studies on the ancient Hebrew calendar as describes in the Bible and here are a few that are helpful:
Articles:
https://guidetothebible.wordpress.com/start-reading-the-book/
http://www.hope-of-israel.org/sabtosat.htm
Videos:
Lunar Sabbaths: Three Months in a Row | Part 1 - The Lunar Sabbath Restored!
9 min long (or faster with the high speed setting):
https://www.youtube.com/watch?v=cUxMRBXuaqI
The Creator's Calendar
9 min long (or faster with the high speed setting):
https://www.youtube.com/watch?v=DbzFGEfgP_8
15 mins (or faster with the high speed setting):
International Date Line Change: The Sabbath Unchanged by Worlds Last Chance Ministries?
https://www.youtube.com/watch?v=7sUyZpM5xls
79 min (or faster with the high speed setting):
Robert-Aaron Richmond explains from scripture how God’s Calendar works:
https://www.youtube.com/watch?time_c...&v=wJq8tKvnemU