This definition of our Third Order is based on the Church's official definition of a Third Order in her Code of Canon Law. A Third Order is not to be confused with a Confraternity (such as the Rosary or Brown Scapular Confraternity) which has its chief purpose the promotion of some public worship. Nor should it be confused with a Sodality or a Pious Association which has for its purpose the exercise of some particular works of piety and charity. Such societies are good in themselves and have been approved by the Church. A tertiary may belong to any or to all of them; but they are not Third Orders. The Third Order entails embracing of a way of life, not the mere practice of some particular work of piety or charity. The lay person embracing this way of life remains a lay person; he does not become a religious, although he does attach himself to one of the great Religious Orders of the Church, in this case the Order of Carmelites. In order to attain and to assure the permanency of this way of life, the Carmelite tertiary has been given, for his guidance, a Papally-approved Rule of Life designed to aid him in obtaining that Christian perfection which is the end and purpose of the Third Order life.
This Rule is the touchstone of the tertiary's life of perfection. It is this that he promises to obey at profession. He stands or falls as a tertiary according to whether or not he has followed its precepts. Just as the Carmelite Friars or Sisters can be judged by their adherence to their particular Constitutions, so can the tertiary by his adherence to this Rule of Life. It should be woven into the very fabric of the tertiary's life. It is the Church's gift to her devout laity, the measuring rod of their tertiary vocation. For seven hundred fifty years it has been helping to produce saints. Faithfully followed, it is the guarantee of a life of perfection in the world.