Rabbi Levi said: If Israel observes Shabbat properly, even one day, the son of David25The Messiah. will come. Why? Because it is equivalent to all the mitzvot. Likewise it says: “For He is our God, and we are the people of His pasture and the flock of His hand; today, would you only heed His voice” (Psalms 95:7).
Rabbi Yoḥanan said: The Holy One blessed be He said to Israel: ‘Even though I set a limit for the end, and it will come whether they repent or do not repent, it will come only at its time. If they repent, even one day, I will bring it not at its appointed time. That is, “today, would you only heed His voice.” Just as we saw that for all the mitzvot, the son of David comes, for the observance of one day of Shabbat, the son of David comes, because Shabbat is equivalent to all mitzvot.
Rabbi Elazar bar Avina said: We find in the Torah, in the Prophets, and in the Writings that Shabbat is equivalent to all the mitzvot. In the Torah, from where is it derived? From the fact that when Moses forgot to tell them the mitzva of Shabbat, the Holy One blessed be He said to him: “Until when do you refuse to observe My commandments…” (Exodus 16:28). What is written thereafter?
“See that the Lord has given you the Shabbat” (Exodus 16:28). In the prophets, from where is it derived? From that which is stated: “The house of Israel defied Me in the wilderness, they did not follow My statutes” (Ezekiel 20:13). What is written thereafter?
“They desecrated My Shabbats” (Ezekiel 20:13). In the Writings, from where is it derived? From that which is stated: “You came down upon Mount Sinai and spoke to them [from heaven and gave them upright ordinances and laws of truth, good statutes and mitzvot]” (Nehemiah 9:13). What is written thereafter?
“You informed them of Your holy Shabbat” (Nehemiah 9:14). The Holy One blessed be He said to Israel: ‘If you merit to observe Shabbat, I consider it for you as though you observed all the mitzvot of the Torah. If you desecrate it, I consider it for you as though you desecrated all the mitzvot.’ Likewise, it says: “Who keeps the Shabbat from its desecration and prevents his hand from performing any evil” (Isaiah 56:2).
When a person observes the Shabbat, he issues a decree and the Holy One blessed be He fulfills it, as it is stated: "If you restrain your walking because of the Sabbath” (Isaiah 58:13). What is written thereafter? “Then you will delight in the Lord” (Isaiah 58:14), just as it says: “Delight in the Lord, and He will grant you the desires of your heart.” (Psalms 37:4). Moreover, everything that you eat in this world is only from the profits, but the principal remains for the World to Come, as it is stated: “I will feed you the inheritance of Jacob your forefather, for the mouth of the Lord has spoken” (Isaiah 58:14).