The General Epistle of James, written by the brother of our Lord, provides ethical instruction for all Jewish people who have become Christians. It is clear and practical in its dealing with Christian behavior.

James 5

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.