My studies indicate the Oath is more in the nature of a contract agreement. Election to Office = Offer / Oath = Acceptance. Keep in mind the original definition of
License is :
n. - 1. Leave; permission; authority or liberty given to do or forbear any act. A license may be verbal or written; when written, the paper containing the authority is called a license.
v.t. - 1. To permit by grant of authority; to remove legal restraint by a grant of permission; as, to license a man to keep an inn.
2. To authorize to act in a particular character; as, to license a physician or a lawyer.