The Establishment Principle holds that there may be a legitimate relationship between the church and the state in a Christian country. This relationship is defined as being one of coordinate jurisdiction, with mutual subordination.
There are other principles of church-state relations. The first is Ultramontanism which gives supreme power to the Pope in all matters. An example of this is the Papal Bull issued by Pius V in 1570 which excommunicated Elizabeth I of England, released Catholics from any allegiance to her, and called upon them to remover her from the throne. While this Bull motivated a few to plots of rebellion or assassination, its main achievement was to turn law-abiding Catholics into potential traitors in the eyes of Walsingham’s security service.
The second is Erastianism. Originally, this was the view that the power to censure sin as well as crime lay with the civil magistrate and that the church had not the power to deny anyone access to the sacraments as a form of censure. It later came to include the power of the magistrate in all religious causes. This was the position of both King and Parliament at the time of the English Civil War. It is the position assumed by all jurisdictions which place the actions of the church under the review of the civil courts.
The third is Voluntaryism. This view denies that there can be a legitimate relationship between church and state. Usually stated as the separation of church and state, this is the position of most Evangelical churches and is the popular understanding of the First Amendment to the Constitution of the United States of America. Its acceptance is founded upon benefits (the residue of previous Establishmentarian thought) generally acknowledged to belong to the church, even though they are challengeable in court. The difficulty with this view is that the church is no different in the eyes of the law from secular voluntary associations or charitable institutions.
The Establishment Principle gives to the Christian civil magistrate a power circa sacra but not in sacris. It recognises that the triune God has ordained civil government and for a Christian government that includes responsibilities about, or concerning, the church: to give it recognition and support. The Christian magistrate has not the powers which the Erastian Principle would give him; he has no powers in holy things. That power, the power of the keys, is given by Christ to the office-bearers whom He has given to His church.
The Establishment Principle is a reminder that the rights which Voluntaries claim for the church can only be secured by the state formally recognising the church to be the institution of Christ.
On the other hand, the Establishment Principle is also a reminder that there is a great work of evangelism to be done before today’s institutions of government might be meaningfully called Christian and entrusted with the external care of the church.