How do Christians who insist upon keeping the 7th day Sabbath explain Acts 15?

In Acts 15 it is recorded that certain men from Judea had come to Antioch and were teaching the Gentile believers that, if they were not circumcised after the law of Moses, they could not be saved. Paul and Barnabbas strongly resisted them: > And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved. When therefore Paul and Barnabas had no small dissension and disputation with them ... - v. 1-2a They were sent/went to Jerusalem to sort out this very issue with the Apostles and elders there and, while reporting on all the things God had done through them amongst the Gentiles: > But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses. And the apostles and elders came together for to consider of this matter.- v. 5-6 After much disputing Peter spoke his piece, explaining how God had made no distinction between Jew and Gentile *in that both are purified by faith* and, in his discourse, he refers to the law of Moses as a yoke on the neck that no one can bear: > Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear? But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they. - v. 10-11 Barnabas and Paul then give more testimony followed by the final summation and declaration on the matter by James, the leader of the Jerusalem council. The council then writes and sends a letter to the Gentile churches in Antioch and Syria and Cilicia. They send this letter with Paul and Barnabas and also send along Judas surnamed Barsabas, and Silas as witnessess to verify that the letter is, in fact, from the Apostles and elders at Jerusalem: > And they wrote letters by them after this manner; The apostles and elders and brethren send greeting unto the brethren which are of the Gentiles in Antioch and Syria and Cilicia: Forasmuch as we have heard, that **certain which went out from us have troubled you with words, subverting your souls, saying, Ye must be circumcised, and keep the law: to whom we gave no such commandment**: It seemed good unto us, being assembled with one accord, to send chosen men unto you with our beloved Barnabas and Paul, Men that have hazarded their lives for the name of our Lord Jesus Christ. We have sent therefore Judas and Silas, who shall also tell you the same things by mouth. **For it seemed good to the Holy Ghost, and to us, to lay upon you no greater burden than these necessary things; That ye abstain from meats offered to idols, and from blood, and from things strangled, and from fornication**: from which if ye keep yourselves, ye shall do well. Fare ye well. - Acts 15:23-29 How do those who insist that the 7th day Sabbath must be kept explain the complete absence of this command in a letter sent to the Gentile church for the express purpose of resolving the issue of which commands these believers should keep?