Summary: Too many professing Christians believe Christ needs a little help to finish His work. They are like the Judiazers Paul fought and like Cain who wanted God to accept His work rather than having the faith of Abel.
Act 15:22 Then pleased it the apostles and elders, with the whole church, to send chosen men of their own company to Antioch with Paul and Barnabas; namely, Judas surnamed Barsabas, and Silas, chief men among the brethren:
23 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:
24 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:
25 It seemed good unto us, being assembled with one accord, to send chosen men unto you with our beloved Barnabas and Paul,
26 Men that have hazarded their lives for the name of our Lord Jesus Christ.
27 We have sent therefore Judas and Silas, who shall also tell you the same things by mouth.
28 For it seemed good to the Holy Ghost, and to us, to lay upon you no greater burden than these necessary things;
29 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.
30 So when they were dismissed, they came to Antioch: and when they had gathered the multitude together, they delivered the epistle:
31 Which when they had read, they rejoiced for the consolation.
32 And Judas and Silas, being prophets also themselves, exhorted the brethren with many words, and confirmed them.
Circumcision was the very first rite of Judaism. It was bringing you into the covenant family. No Jewish family would consider not doing this to their male child and try to raise them in the Law. Without the foundation the rest would be useless. Gentile converts to Judaism were required to be circumcised under the Law, which is probably what sparked the issue the Council addressed.
That said, it is very clear that the Gentiles were not required to keep any of the Mosaic Code to be saved/sanctified if they were not required to lay the foundation of circumcision. Though these men were Jewish they said the Holy Ghost told them what to say to the Gentile believers.
We do not have to keep feasts or Sabbaths of any kind. Baptism did not replace circumcision since circumcision was no longer required. Besides, if that were true girls were not circumcised so they would not be baptized either In essence, circumcision was a blood covenant between God and man. The shedding of hymeneal blood on the wedding night was the blood covenant between man and woman.
All those groups that try to mingle the OT and the NT or Law an Grace are practicing the very thing Paul fought against throughout his writings. Indeed, it is a grave error that Paul warned the Galatians that if they were circumcised, they would have to keep the whole Law.
Gal 5:1 Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.
2 Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing.
3 For I testify again to every man that is circumcised, that he is a debtor to do the whole law.
4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
No one can keep the whole Law, not even the Jews as there is no temple to sacrifice in and has not been one since 70 AD. Without the shedding of blood there is no remission of sin so if you want to keep the Law you are doomed because if you sin in one point of the Law you break the whole Law. Anything else you do is a waste of time and profits you nothing in the courts of Heaven.
Remember Cain? He wanted a Frank Sinatra kind of sacrifice. Cain did it his way and offered up the fruit of his labors and was rejected. A Gentile trying to keep the Law is doing the same thing. In fact, it is a slap in Christ's face making His sacrifice not quite enough to get the job done. He needs our rituals and vain keeping of the Law to complete the work He came to do.
He came to set us free from sin and to fulfill the Law allowing us to walk in freedom as sons and daughters. Yet, we enslave ourselves to rites and rituals of men who failed to grasp what the Cross meant. Faith and faith alone justifies us before God. Jesus paid it all and we received the gift for free when we turn from our Cain religions to the faith/trust in Christ.