Are you sure that there are no references that make the commandments desirable?
Remember that it was James who spoke the words in Acts 15:20 that you quoted above. But in his own epistle, James says: “but you be doers of the commandment and not hearers only!” He also says: “whosoever shall keep the law, and offend one point, he is guilty of all. For He that said Do not commit adultery, said also Do not kill”. He even goes ahead and says that transgressors of the law shall be judged by the law of liberty (whatever interpretation this may have – judgment is there). And John says "For this is the love of God, that we keep His commandments". To which commandments was John referring? Undoubtedly, to the commandments of God which, when transgressed, result in sin. The apostle Paul tells us plainly which commandments these are. He writes that he would not have known what sin was except the law told him, "You shall not covet". This directly references one of God's Ten Commandments! John also taught the importance of God's Commandments. In revelation he writes: "Blessed are they that do his commandments that they may have right to the tree of life". He states further in Revelation: "Here is the patience of the saints. Here are they that keep the Commandments of God and the faith of Jesus Christ." And in 1John, he explains that if anyone says he knows Christ, but doesn't keep His commandments, he is a liar, and the truth is not in him. Could anything be more clear?
You are wondering why we are alone in this.
Well, though we have many traditions that render as unique, I don’t think that we are alone in this case. Your church honors the Sabbath. Other churches also honor the Sabbath. But why do you think are you honoring the Sabbath? It is simply because it is one of the Ten Commandments for God’s obvious reasons. The only difference between you and us is that we honor it much more deeply than you do! So why are we honoring it to this extent? Other than my arguments so far, our observance of the Sabbath is based on the following:
1. The Ten Commandments that were written by “the fingers of God” on stone tablets and given to us.
2. The 66th order in our Book of Synodos (which one of the books of church order) which says that we should observe both Saturday and Sunday similarly.
3. The Counsel of Debre-mitmaq that was held in 1450, chaired by King Zara’ Yaqob, summoned all the heads of churches and monasteries and Tewahido scholars of the nation and that declared Saturday and Sunday to be observed equally.
4. The Ethiopian Fitiha Negest, which is the “cannonum regum” or the Law of kings, that states in its article 19, that we should observe both Saturday and Sunday. It also states that we should observe Saturday not the way Jews are observing it but the way Christians are. Therefore, we are happy of the way we are observing the Sabbath because whatever we do on this day is Christian and is indicative of the fact that we are giving it much more honor.
5. The books of the lives of saints Tekle-haymanot, Filipos, Ewostatheos, Zena-marqos, Aba Giorgis of Gasicha, etc. that underline the importance of observing the Sabbath. Aba Giorgis, in his famous ‘book of mystery’, has also indicated the importance of the two Sabbaths, Saturday and Sunday.
Remember the Sabbath and keep it holy!!