This letter was in regard to the Jews wanting the gentiles to observe the law. These holy days were something that were unique to judaism. This letter was directed toward this issue of the gentile having to observe the things of the Law or not. There is no mention in this letter of the ceremonial cleansing, the dietary laws, or the holy days. Things that should be essential according to you, but it seems the Holy Spirit saw otherwise. That still doesn't invalidate my point. You're trying to say that the holy days were not taught because the holy days were not referenced in the letter. The ten commandments for the most part were also not mentioned in the letter. They were as much a part of the law, if not more so, then the holy days. By your logic, gentile converts weren't being taught to refrain from killing, worshipping false Gods or worshipping idols.
Your statement that the holy days were unique to Judaism is perhaps technically accurate, but biblically there are examples of non-Jews not only observing, but worshipping at God's Holy Days:
Joh 12:20 And there were certain Greeks among them that came up to worship at the feast:
Also, verse 21 is not even included in the letter
It doesn't matter. Verse 21 was an explanation of WHY they didn't include MORE in the letter:
Act 15:20 Instead, we should write a letter telling them to keep away from things polluted by false gods, from sexual sins, from eating the meat of strangled animals, and from eating bloody meat.
Act 15:21 After all, Moses' words have been spread to every city for generations. His teachings are read in synagogues on every day of worship.
For generation people had been learning about the Holy Days. This was the normative cultural and scriptural thing to do. It was commanded by God in the only holy scriptures they had. Of course they were observing them. The only thing that makes you think they weren't is that your are looking backward under the prism of your current beliefs and current tradition.
In Acts 21 we have yet another example of this. Paul comes to Jerusalem and the saved Jews are upset because he is telling others not to observe the Law of Moses and James says this in verse 25:
"But concerning the Gentiles who have believed, we wrote, having decided that they should abstain from meat sacrificed to idols and from blood and from what is strangled and from fornication."
Here James is restating the point that the Gentiles need not walk according to the customs, which would include the Holy Days and dietary laws, except for those mentioned in the letter.
Once again, why send them a letter at all? If they were to observe the customs and Laws as you say, then there was no need for the letter for this is what you say they were being taught anyway. Or if what you say is true, why not say so in the letter to clear up the confusion that was arising? They were having the same issues we are talking about now. They cleared it up by saying to just observe these essential and you will do well. If observing the feasts were essential, as you say, would that not have been mentioned? Plus, Acts 15:21 was NOT included in the letter nor is it mentioned in Acts 21.
JM