And Acts tells the story of Christianity being embraced by other than Jews. That's what the whole of that letter is about. — why do you add more than what the Holy Spirit set forth?
It was detailed as essential by Yeshua himself in two chapters in Matthew, and expressly in detail by John in his first epistle, and by Paul in Romans 2.
Mark 2:27,28 Then he said to them, "The Sabbath was made for man, not man for the Sabbath. So the Son of Man is Lord even of the Sabbath." I trust the Holy Spirit is in agreement with the Lord of the Sabbath in this matter, and seeing as how they said For it has seemed good to the Holy Spirit and to us to impose on you no further burden than these essentials: that you abstain from what has been sacrificed to idols and from blood and from what is strangled and from fornication they would have included the Sabbath as essential if it were.
Earlier in Acts chapter 15 it details how the matter got brought up to the council:
When they came to Jerusalem, they were welcomed by the church and the apostles and the elders, and they reported all that God had done with them. But some believers who belonged to the sect of the Pharisees stood up and said, “It is necessary for them to be circumcised and ordered to keep the law of Moses.”The apostles and the elders met together to consider this matter.
After there had been much debate, Peter stood up and said to them, “My brothers, you know that in the early days God made a choice among you, that I should be the one through whom the Gentiles would hear the message of the good news and become believers. And God, who knows the human heart, testified to them by giving them the Holy Spirit, just as he did to us; and in cleansing their hearts by faith he has made no distinction between them and us. Now therefore why are you putting God to the test by placing on the neck of the disciples a yoke that neither our ancestors nor we have been able to bear? On the contrary, we believe that we will be saved through the grace of the Lord Jesus, just as they will.”
The whole assembly kept silence, and listened to Barnabas and Paul as they told of all the signs and wonders that God had done through them among the Gentiles.
The key point in Acts 15 was that the new believers could not learn Torah in a weekend.
For that reason they stated the minimum needed to keep out of trouble, since they were expected to be hearing Moses read every Sabbath day, where they would come up to speed in much the same way that the House of Judah had in their youth.
Grace is the writing of Torah on our hearts, so that the keeping of commandments is our desire (back to Romans 2).
[12] For as many as have sinned without law shall also perish without law: and as many as have sinned in the law shall be judged by the law;
[13] (For not the hearers of the law are just before God, but the doers of the law shall be justified.
[14] For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:
[15] Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;)
They did include the Sabbath as essential. Read Acts 15!
[19] Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
[20] But that we write unto them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood.
[21] For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day.
More importantly Yeshua called Torah as a whole essential for all, until the Earth and Heavens pass away (Mat 5)
[17] Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
[18] For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
[19] Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven.