In contemporary terms, ecclesiastical law is the internal set of laws, rules, regulations and statutes that a church codifies to administer its own operations. These laws are permutations of the original ecclesiastical law — also called English law or canon law — that once governed much of the Roman Catholic empire when the Church was the arbiter of judicial decree. In much the same way that today’s civil and criminal laws are derived from government, ecclesiastical law originated from the dictates of religious councils, beginning in the 1st century B.C.E. From there, they developed the foundations for what would later become much of the civil law that developed in England during the Renaissance and the Enlightenment periods.
In the 1st century, council-based systems for many of the world’s leading religions began establishing the sets of canonical rules and laws that would form the basis for numerous rites and doctrines. Of course, this does not mean that ecclesiastical law should be confused or conflated with religious doctrines, such as the Torah, the Bible, the Koran or others. Those religious codices are intended for parishes and practitioners. Canonical and ecclesiastical law is intended to govern the behavior and practices of clergy and high church offices with internal matters of policy and process.
The Roman Catholic Church established one of the widest and most complex sets of ecclesiastical law in recorded history. With the establishment of the Latin Rite — and later the churches that would comprise the Eastern Orthodox bloc — decrees governing all manner of religious practice, priestly comportment and a host of internal topics were written by the Church's leading scholars and administrators. In 17th century England, the growing tensions between Roman Catholic and Anglican forces spilled out onto the streets, sparking the English Civil War. As a result of this conflict, many of the elements of ecclesiastical law were appropriated by Anglican leaders during their time of rule, which were then incorporated into the secular development of English common law that arbitrated civil and criminal matters.
By the 19th century, more than 10,000 decrees and rules existed in various manifests and compendiums that constituted Roman Catholic corpus juris — canon law. This body of codes and laws dealt with nearly every topical matter that the Church had encountered during a millennium of jurisprudence. It soon become apparent that many of the rules and decrees that comprised ecclesiastical law were directly contradictory in nature. This fact led the Roman Catholic Church to establish a single volume of canon law free from errors, obsolescence and contradiction, that still exists today.