Shabbat was given to Israel shortly before they arrived at Mt. Sinai when they were told not to gather man ("manna") on the Seventh Day of the week. However, the 'Avot (Abraham, Isaac, and Jacob) had already intuited all the commandments of the Torah according to the Sages.
Were they not to be the light of the world and share the worship and knowledge of the God of Abraham OR hide it under a basket?
Well, yes and no.
Non-Jews are actually forbidden to observe Shabbat (at least with regard to the prohibitions;
It depends on whether one follows the dictates of the Jewish tradition or not. I would say that biblically speaking those who join themselves to Israel through Christ become partakers of the blessings promised to Israel, including the blessing of the sabbath.
Eph 2:12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
Eph 2:13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ
Shabbat was given to Israel shortly before they arrived at Mt. Sinai when they were told not to gather man ("manna") on the Seventh Day of the week. However, the 'Avot (Abraham, Isaac, and Jacob) had already intuited all the commandments of the Torah according to the Sages.
The article presents a number of interesting passages about sabbath observance even before Abraham.
Here’s a note on the subject from the Center for Judaic-Christian Studies
Is the Sabbath Made for Man, or Not?
AUTHOR: Dwight A. Pryor
JESUS SAID, “The Sabbath was made for humankind” (Mark 2:27 NRSV). But for centuries the Church has argued that the Sabbath was made for Jews. The seventh-day commemoration of the creation is not for Christians, said the Church Fathers, because it was superseded by the eighth day of resurrection and the new creation in Christ. So Jews worship on Saturday but Christians worship on Sunday.
Without dispute, the Sabbath is precious to Israel and uniquely and indelibly connected to the Jewish people. Following the Exodus from Egypt, God brought Israel to Mt. Sinai, and there like a loving bridegroom invited her to become His bride—i.e., to affirm and renew the covenant He first cut with Abraham. After hearing the Ten Words read—a ketubah of sorts—Israel with one voice affirmed: “All that Adonai has spoken we will do!” (Exo 24:7).
As an eternal sign (’ot olam) of this perpetual covenant, God gave Israel the precious gift of Shabbat. Like a wedding ring, it will forever symbolize their exclusive covenant union (31:16-17). This is why the prophets like Jeremiah could view Sabbath observance as a singular sign of Israel’s covenant fidelity or lack thereof. Whenever Israel removed her ‘wedding ring’, invariably she was going whoring after other ba’alim or husbands.
So important was the Sabbath to the vitality and viability of this covenant relationship with the Lord that nonobservance required the offender to be cut off from the community (31:14). Honoring the seventh day took precedence even over construction of the Mishkan or Tabernacle (35:2-3ff). Honoring God by sanctifying time has a higher priority than constructing Him a sanctuary in space.
So yes, the Sabbath is uniquely for the Jews. As oft noted, it has kept Israel even more than Israel has kept it. The Jewish people are the “personal property” of the King (19:5); even so they treasure Shabbat as a Queen. IN WHAT SENSE THEN can we say that “the Sabbath is for humankind”—including Christians who also wish to honor God by remembering Shabbat?
A clue to the universal character of the Sabbath can actually be found in the Ten Commandments, of which there are two records: Exodus 20 and the repetition thereof in Deuteronomy 5. The two versions essentially are identical except for one word. One enjoins “Remember” (zachor) the seventh day and the other to “Observe” (shamor) it.
Note that the reason given for “remembering” the Sabbath is the creation (Exo 20:11). Whereas the covenant obligation to “keep” or “observe” the Sabbath stems from the redemption from Egypt (Deut 5:15). Obviously both aspects are relevant to Israel, but perhaps at another level we see here a basis for humankind honoring the Sabbath as well. After all, long before the Mosaic covenant with Israel was struck at Sinai, God created adam (humankind) in the Garden and then ceased from His labors. Shabbat was a universal creation principle before it became a particular covenant precept.
For everyone created in the image of God, therefore, surely it is good and wise to emulate our Creator by resting from our labor and to honor Him by sanctifying the seventh day. Properly practiced, in joy, Shabbat can restore the soul, build up the family and draw us closer to God.
A careful examination of the gospel accounts reveals that Yeshua observed the Sabbath as a devout Jew. (After all, to do otherwise would have been to sin). Against some of his supercilious critics, wont to impose stifling restrictions, Jesus stressed that the Sabbath is intended by God to be life-affirming and a blessing. It is for man.
The first church, like Jesus, continued to honor the Sabbath and to worship at the synagogue. But as Shabbat ended they would gather from house to house “on the first day of the week” (Acts 20:7) for instruction from the apostles and for fellowship, and to set aside contributions for the needy (1 Cor 16:2). In other words, they honored the Creator and God of Israel on the Sabbath as well as assembled on Sunday in remembrance of their risen Lord. These need not be mutually exclusive.
Shabbat should be an enormous blessing for everyone, for Jew and Christian, for families and communities. The Sabbath is for humankind. You have Jesus’ word on it!