Halakha Yesaya 56:2: Mishneh Torah, Sabbath, Kitzur Shulchan Arukh & Arukh HaShulchan

Both of these two—Shabbat and idolatry—are, each one, of the same weightiness as all the other commandments of the Torah. And Shabbat is the sign between the Holy One, blessed be He, and us forever. Hence anyone who transgresses the other commandments is surely included among the evildoers of Israel. But one who desecrates Shabbat in public is surely like an idolater. So both of them are like (gentile) idolaters in all of their matters. Therefore the prophet praises [one who observes Shabbat] and says (Isaiah 56:2), "Happy is the man who does this, and the man who holds fast to it; who keeps Shabbat and does not profane it, etc." And the reward in this world—beyond the reward that is saved for the world to come—[for] anyone who observes Shabbat according to its law, honors it and delights [in] it according to his ability is already explicit in the tradition. As it is stated (Isaiah 58:14), "Then you can delight in the Lord; and I will set you astride the heights of the earth, and feed you the heritage of your father Jacob—for the mouth of the Lord has spoken."

Therefore the prophet offers praise and says, "Fortunate is the man who does this, and the son of man who maintains this, he who preserves the Shabbos from desecration etc."¹⁴Isaiah 56: 2. The prophet describes the reward of one who keeps the Shabbos in accordance with Halachah,¹⁵i.e., Torah laws. and honors it and delights in it to his utmost ability. He will be rewarded in this world besides the great reward reserved for him in the World to Come, as it is said:¹⁶Isaiah 58: 13. "If you restrain your feet [from going out of the techum]¹⁷Techum means boundary. You must not walk more than 2,000 amos past the city limits; see Chapter 95 for exact details. and abstain from doing your business on My holy day and you proclaim Shabbos a delightful day, and the sanctified of God, honored, and honor it by not engaging in your weekday activities, and abstain from pursuing your business affairs and (from) speaking words [pertaining to your weekday needs];¹⁸See Rashi, Maseches Shabbos, 113b. Rabbeinu Tam maintains that this is included in the prohibition of “pursuing your needs,” and explains that on Shabbos one should not engage in too much small talk [Yerushalmi]. The Rambam, Shabbos 24: 1–4 and Shulchan Aruch 307: 1 include both the above in “vedaber davar.” If you enjoy telling stories you may do so (Rema 307: 1). then you will delight yourself before Hashem, and I will cause you to ride over the heights of the earth, and will nourish you with the inheritance of Jacob, your father, for the mouth of God has spoken."¹⁹Isaiah 58: 14. ²⁰Rambam (conclusion of laws of Shabbos).

And the prophets, when they rebuked Israel for violating the Torah, specifically rebuked them for the desecration of the Sabbaths themselves. It says: "Blessed is the man who does this... who keeps the Sabbath from desecrating it and keeps his hand from doing any evil" (Isaiah 56:2) — meaning, the merit of observing the Sabbath will cause him not to commit any evil. And furthermore, it says: "Everyone who keeps the Sabbath without desecrating it and who holds fast to My covenant" — meaning, the covenant of the Torah. Thus, it is explicitly stated that one who desecrates the Sabbath is considered to be breaking the covenant of the Torah.