With the commandment to “Commemorate the day of Shabbat to sanctify it” (Shemot 20:8), we are enjoined to recall the foundations of faith. This is why the mitzva of Shabbat is the fourth of the Ten Commandments. First we are commanded to believe in God and know Him, as it states: “I am the Lord your God Who brought you out of the land of Egypt, the house of bondage” (Shemot 20:2). Following this we are commanded not to worship foreign gods: “You shall have no other gods besides Me. You shall not make for yourself a sculptured image, or any likeness… You shall not bow down to them or serve them” (ibid. 3-5). The third commandment is to honor His name and not to swear falsely. The fourth commandment is about Shabbat, the day that expresses the foundations of our faith in the world (Ramban, Shemot 20:7). Zohar states that all the principles and secrets of faith are linked to Shabbat (II 92:1; III 94:2, 288:2).
We recall two fundamentals of faith on Shabbat. The first is the creation of the world. Shabbat attests that the Creator made the world in six days and rested on the seventh. Ever since then, He continues to give the world life and sustain it. The second fundamental is that God took His people out of Egypt. By doing so, He made clear to all that in addition to having created the world, He also supervises and manages it, punishing the wicked and rewarding the righteous. He chose Israel to be His people, through which His providence is made manifest in the world.
The Sages tell us that the mitzva of Zakhor entails invoking Shabbat throughout the week, by preparing for it. Similarly, the Levites in the Temple would preface the singing of the daily psalm with the formula: “Today is the first/second/etc. day of before Shabbat.” This tells us that the weekdays are not days in their own right, but rather draw their meaning and value from Shabbat. It is indeed a fact that in Hebrew, the holy tongue, days are numbered in relation to Shabbat – the first day, the second day, etc. This contrasts with other languages, such as English and French, in which each day has its own name – generally named for some ancient deity – and has no connection to Shabbat (Ramban, Shemot 20:7).
The primary way in which we fulfill the mitzva of Zakhor is through kiddush, in which we invoke the central themes of Shabbat in brief. The Sages instituted that kiddush be recited over a cup of wine and shortly before a meal, so that Shabbat would be mentioned at a time of joy and pleasure, as Scripture states: “Call Shabbat ‘delight’” (Yeshayahu 58:13; see below 6:3 and 6:10).
Although we fulfill the basic obligation of Zakhor through kiddush, the mitzva in principle is to sanctify the entire day. The Torah states “Commemorate the day of Shabbat to sanctify it,” implying that the entire day should be set aside for holy matters – Torah study and attending lectures by Torah scholars (Ramban, Shemot 20:7; see below 5:1-5).