The Letter to the Galatians
There is a scholarly consensus that Galatians was written by Paul, however, there is not a consensus as to the date of writing, with estimates running from the late 40s to the late 50s.Galatians 1-2 is mostly biographical, and to date the book of Galatians it is necessary to fit the events described there into the overall New Testament timeline. In Gal 1:17, Paul describes his stay in Arabia and Damascus after his conversion. He says that after three years he went to Jerusalem (Gal 1:19), an event corresponding to Acts 9:26-29, which we have dated to 36 A.D. He then returned to Tarsus in Cilicia (Acts 9:30, Gal 1:21). His next return to Jerusalem was 14 years later, with Barnabas (Acts 11:30, Gal 2:1), in 49 A.D. (Remember to add inclusively, without a zero). Paul's first missionary journey followed, and it was during this journey that he founded the Galatian churches. This was followed by the controversy over requirements for gentile believers that led to the Jerusalem Council of 50 A.D.
The letter to the Galatians does not mention the Jerusalem Council, and the omission is telling. Paul is extremely emotional in Galatians in his opposition to the "Judaizers", Jewish Christians who followed him to Galatia and had been teaching the gentile believers there that they needed to be circumcised and follow the law of Moses. Paul was adamently opposed to that idea, and it was this controversy that led to the Jerusalem Council of 50 A.D., described in Acts 15. The council's verdict went essentially in Paul's favor, indicating that gentiles did not need to be circumcised or follow the law of Moses, but requiring them to abstain from food offered to idols, from eating meat with blood, and from sexual immorality (Acts 15:29), restrictions necessary to allow fellowship between Jewish and gentile Christians.
It seems likely that Galatians was written just prior to the Jerusalem Council, when the controversy over gentile believers was white hot. It could hardly have been written afterward, for then Paul would have appealed to the tremendous authority of the council, with a decision backed by James and all the Apostles. Galatians is then dated to 50 A.D., and it becomes the earliest surviving letter of Paul.