The Book of James was written around 49 AD by James, a leader in the very first Christian church, the Church of Jerusalem.
Members of the Jerusalem church had been removed from the city and spread out to other Roman provinces because of persecution. The letter aims to encourage them during these difficult times. James explains to them that their faith will change not only their conduct but also their character. He gives his readers several tests against which they can measure their faith in Christ. If a Christian fails these tests then their faith is dead.
James 5:12
"But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation"