Why did Paul hurriedly write the book of Galatians?

Paul hurriedly wrote this epistle after receiving word that the Gentile churches he had established in Asia Minor were being tempted by legalism. Judaizers were deluging them, trying to bring these Gentile believers under the law and into legalism. He wrote to correct this threat.

Les explains that Paul had already been up into Asia Minor on his missionary journeys, where he had established Gentile churches. When he got word that they were being tempted with legalism, he hurriedly wrote this little epistle. The churches were being deluged with Judaizers who were trying to bring these Gentile believers under the law, legalism. That situation prompted Paul to write to them.

Galatians 2:1

Then fourteen years after I went up again to Jerusalem with Barnabas, and took Titus with me also.

Who did Paul meet with in Jerusalem in Galatians 2, and what did he have to do?

Paul met with Peter, James, John, and the other church leaders in Jerusalem. He had to give an account of what he had been preaching to the Gentiles, and he went up by revelation and clearly communicated his gospel to them.