Circumcision was induction into the Mosaic Law.
But nice of you to ignore not only the conversation leading up to the letter, but the letter itself:
For it has seemed good to the Holy Spirit and to us to lay on you no greater burden than these requirements: that you abstain from what has been sacrificed to idols, and from blood, and from what has been strangled, and from sexual immorality. If you keep yourselves from these, you will do well. Farewell.
Now what does "If you keep yourselves from these, you will do well" mean unless it is to say that this is all that they need to do life-wise to be Christians? (Not that they wouldn't do good works, as James says faith w/o works is dead, but that these are the requirements to keep spiritually clean, the answer to what sort of life do I live to be conducive to godliness.)
Now, with that in mind, answer this: does my observance or lack of observance of any holiday/feast/fast impact my salvation? Does it impact my righteousness, the righteousness that is not mine but that of Jesus?
You speak of the Halakhah Laws. Do you know what they are? What exactly is James telling the gathering? He is agreeing that the Gentile converts should no longer be required to undergo circumcision.........and they would do well to eat no blood, eat no meat of strangled animals, eat no food offered to idols and keep themselves sexually pure.
Where does he tell them no longer to observe the Feasts and Sabbaths that Paul and John continued to do throughout the New Testament (and their disciples continued to observe into the second and third centuries)?
The Halakhah Laws are found in Leviticus, Chapters 17 & 18].....and they deal with "Strangers among us" as the Jews of the Jerusalem Church still viewed the Gentiles to be. It had only been recently that the Church even considered them for salvation and any type of evangelizing [Acts 11:18-19]. This was the bone of contention that got Paul so riled up [Acts 15:2] and caused him to seek this council and have it out with James.....once and for all.
James had been sending out "circumcision patrols" to Asia minor, interfering with Paul and his ministry [Galatians 2:12] and Paul had just about had it! He even suggests that these folks from Jerusalem (he calls them agitators) go castrate themselves! Here is the "New International version for clarity: [Galatians 5:10-12] 10I am confident in the Lord that you will take no other view. The one who is throwing you into confusion, whoever that may be, will have to pay the penalty. 11Brothers and sisters, if I am still preaching circumcision, why am I still being persecuted? In that case the offense of the cross has been abolished. 12As for those agitators, I wish they would go the whole way and emasculate themselves!
The Council dealt with adult, Gentile convert circumcision.....and nothing else. The Feasts, the Sabbaths, the dietary Laws were not an issue! The Halakhah Laws dealt with how the "Strangers among us" should conduct themselves.....living with and observing the Feasts of Israel. Here's a snippet:
[Leviticus 17:10-16]10“ ‘I will set my face against any Israelite or any foreigner residing among them who eats blood, and I will cut them off from the people. 11For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one’s life.c 12Therefore I say to the Israelites, “None of you may eat blood, nor may any foreigner residing among you eat blood.” 13“ ‘Any Israelite or any foreigner residing among you who hunts any animal or bird that may be eaten must drain out the blood and cover it with earth, 14because the life of every creature is its blood. That is why I have said to the Israelites, “You must not eat the blood of any creature, because the life of every creature is its blood; anyone who eats it must be cut off.”
15“ ‘Anyone, whether native-born or foreigner, who eats anything found dead or torn by wild animals must wash their clothes and bathe with water, and they will be ceremonially unclean till evening; then they will be clean. 16But if they do not wash their clothes and bathe themselves, they will be held responsible.’ ”
And the clincher: [Exodus 12:48-49]48“A foreigner residing among you who wants to celebrate the Lord’s Passover must have all the males in his household circumcised; then he may take part like one born in the land. No uncircumcised male may eat it. 49The same law applies both to the native-born and to the foreigner residing among you.”
Paul and Barnabas were allowing uncircumcised, adult male Gentiles to partake of the Passover with them in Antioch......and the "Church" (can you say Pharisees?) wanted it stopped!
The Feast Days, Sabbaths and Dietary restrictions were never a subject dealt with by the council.