That we are living in unprecedented times hardly needs to be stated. It is hard to believe that less than three months ago we in the west were living in blissful ignorance, oblivious to what lay just around the corner. We may have heard vague reports of something amiss in China, but we continued along our merry way. As the world came to a virtual standstill time slowed down, if not scientifically, then at least in our perception of it. (And with time being relative isn’t that what matters?)
It is not uncommon to lose track of time often forgetting what day of the week it is, sometimes not realizing that it is almost Shabbat. This despite the constant signals that surround us - newspapers, radio, television, computers and the like that clearly indicate the date and time on a non-stop basis. Luckily, if we do lose track of time it is very easy to quickly get back on track.
The Sages of the Talmud had to deal with a more serious loss of time. Outside of a sundial there was little to let people know what time it was. And while that might help in figuring out the latest time to say the shema or shemoneh esrei, it did little in terms of letting one know what day of the week it was. It was a stroke of genius that our Sages instructed us to end davening each morning by announcing which day of the week it was. Like all our minhagim there is both deep religious meaning and a very practical reason for our practice. This simple idea helped to ensure (provided we were paying attention to what was said) that we not miss Shabbat. With our lives currently turned upside down it is not hard to realize how that might happen. And that is while one is at home in the 21st century. How much more would this be so for one travelling alone in the third?
“Rav Huna said: One who was walking in the desert, and he does not know when Shabbat is, counts six days and observes one day [as Shabbat]. Chiyya bar Rav says: He observes one day [as Shabbat and then] counts six” (Shabbat 69b). The Gemara explains that Rav Huna looks to “the creation of the world”, where Shabbat follows six “days” of creation. Shabbat is the culmination of the week, where we withdraw from our creative activities. But in order for Shabbat to be shabbat we must first have six days of “work”. Chiyya bar Rav’s focus is on man. Born from the last act of creation on Friday afternoon, man first experienced Shabbat and only afterwards the six days of the work week and hence this confused soul in the desert must first observe shabbat.
We find two very different reasons in the aseret hadibrot as to why we must observe shabbat. In parshat Yitro we are told that we must observe shabbat “For in six days the Lord made heaven and earth and sea, and all that is in them, and He rested on the seventh day; therefore the Lord blessed the Shabbat day and hallowed it”(Shemot 20:11).
Yet 40 years later when Moshe recounts the Divine revelation at Sinai there is a very different reason for shabbat observance. We must “Remember that you were a slave in the land of Egypt and the Lord your God freed you from there with a mighty hand and an outstretched arm; therefore the Lord your God has commanded you to observe the Shabbat day” (Devarim 5:15).
The slave who left Egypt needed no reminder that he was a slave. Working seven days a week, he longed for a day off. Shabbat was a great gift – and any reason would do. But this slave needed plenty of reminders that there is a G-d who runs the world and that G-d makes demands on people. He had to be reminded that in six days the Lord made heaven and earth and sea.
The Jew who wandered in the desert needed no reminder of G-d. With food falling from heaven, clothes remaining as new and feet not swelling (Devarim 8:4) the presence of G-d was palpable. Life was so easy, it was the notion of slavery, the tragedy of being subjugated to man, which one had to be reminded of – and warned not to do to others.
Shabbat has both a theological and a social component; it is meant to strengthen our relationship with G-d and with our fellow man. It is a day to remind ourselves of our limitations, that much as we may often forget we are not G-d. We are mortal and should lead our daily lives with that in mind. Mortal man must be humble man and humble man does not make other people work seven days a week.
The halacha has accepted the view of Rav Huna. Shabbat is first and foremost our affirmation of G-d as Creator of the world. It is the recognition that all are subservient to G-d that will ensure we recall that man has only one Master and that “they are slaves to Me and not slaves to My slaves”.
 While the day, (lunar) month and year all are connected to aspects of nature the seven-day week is a biblical invention, demonstrating G-d’s mastery of nature. While the author has a different take I found this recent article of interest.
 Absent religious significance, no matter how widely observed, a practice is no more than a non-binding convention. Hence the ruling of Rav Moshe Feinsten that one who accepts Shabbat early only in the summer cannot be said to have a minhag to bring in Shabbat early. Convenience yes, minhag no.
 The Ramban claims that doing so is a fulfilment of the mitzva of “zachor et yom hashabbat lekadsho”. The need to remember something is most acute when it is missing. Hence we must remember the Shabbat on the other six days of the week. While we today may understand this mitzva as requiring one to be cognizant of Shabbat each and every day, for the ancients there was a much more practical reason for this mitzva.
 As a practical matter, the Gemara goes on to explain that unless he knows that this day cannot be shabbat i.e. he can't recall if he left home on a Wednesday or Thursday he must observe all the strictures of Shabbat every day. Of course, anything necessary to find his way home (if he is actually lost) would be allowed every day including the day he observes as Shabbat because of pikuach nefesh. This debate is on which day he should make kiddush and havdallah.