Halakhah sa Deuteronomio 5:14: The Sabbath Epistle & Mishneh Torah, Sabbath

Here are honest witnesses that the day begins with dusk. Similarly for all the holidays and the Sabbath, for all are “appointed seasons of God, holy gatherings” (ibid. 23:4). Only the Sabbath is called “a Sabbath for God” (Exodus 20:10, Deuteronomy 5:14), for God rested during Creation. Since both the year and the day are dependent on the sun, for both motions are similar one to another, therefore the seventh year is comparable to the Sabbath day. Hence it is also written with regard to the seventh year “a Sabbath for God” (Leviticus 25:2). Therefore, just as the Sabbatical year begins with the autumn season, so the beginning of the Sabbath day is in that period of the day corresponding to autumn, which begins with dusk.

The Sages forbade moving some things on Shabbat in the way that he does on [weekdays]. And for what reason did they [promulgate] this prohibition? They said, "And just like the prophets prohibited and commanded that your going on Shabbat not be like your going on [weekdays] and that the speech of Shabbat not be like the speech of [weekdays]—as it is stated (Isaiah 58:13), 'and speak a word'—all the more so should the carrying of Shabbat not be like the carrying of [weekdays. This would be] so that it not be like a [week]day in his eyes, and he come to pick up and fix vessels from one corner to another or from one house to another, or store rocks, and that which is similar to it. As he is surely idle and sits in his house and will seek something with which to occupy himself. And it will come out that he would not have rested, and would nullify the reason [for Shabbat]; as it is stated (Exodus 22:12 and Deuteronomy 5:13), 'in order that he will rest.'"