"To swear an oath" means to make a solemn promise, usually in a formal or legal setting, where you guarantee to do something or adhere to certain rules or principles. Full definition
And it became obvious that the proposition that scientists swear an oath of ethical behavior is a controversial and almost overwhelming concept. (sciencemag.org)
The government doesn't pay you, taxpayers don't pay you and you haven't sworn an oath to anybody. (citifmonline.com)
Mormons do NOT practice polygamy so there will NOT be a plethora of first ladies!!!! If Romney wins, he will not swear his oath on the Book of Mormon. (religion.blogs.cnn.com)