This 67th book of the Bible is a book of the Bible that all the apostles and all the elders jointly wrote.
Acts 15:19-21
New International Version
19 “It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God. 20 Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood. 21 For the law of Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath.”
The writing came from the suggestion of Apostle James, as a result of the the debates and argument that the gentiles had to be circumcised to be saved.
So they decided to write this letter to the gentiles in Antioch, Syria and cilicia.
Watch the full answer to the Question but Bro Eliseo from the link