It is through Apostolic Succession that the Orthodox Christian Church is the spiritual successor to the original body of believers in Christ that was composed of the Apostles. This succession manifests itself through the unbroken succession of its bishops back to the apostles.
The unbrokenness of apostolic succession is significant because of Jesus Christ's promise that the "gates of hell" (Matthew 16:18) would not prevail against the Church, and his promise that he himself would be with the apostles to "the end of the age" (Matthew 28:20). According to this interpretation, a complete disruption or end of such apostolic succession would mean that these promises were not kept as would an apostolic succession which, while formally intact, completely abandoned the teachings of the Apostles and their immediate successors; as, for example, if all the bishops of the world agreed to abrogate the Nicene Creed or repudiate the Holy Scripture.
The Orthodox believe that their teachings today are the same as or are in essential harmony with the teaching of the first apostles. This form of the doctrine was formulated by Irenaeus of Lyons in the second century, in response to certain Gnostics. These Gnostics claimed that Christ or the Apostles passed on some teachings secretly, or that there were some secret apostles, and that they (the Gnostics) were passing on these otherwise secret teachings. Irenaeus responded that the identity of the original Apostles was well known, as was the main content of their teaching and the identity of the apostles' successors. Therefore, anyone teaching something contrary to what was known to be apostolic teaching was not, in any sense, a successor to the Apostles or to Christ.
In addition to a line of historic transmission, Orthodox Christian churches, as also the Non-Chalcedon Orthodox churches, additionally require that a hierarch maintain Orthodox Church doctrine, which is that of the Apostles, as well as communion with other Orthodox bishops. The Orthodox Christians have at times permitted clergy ordained by Roman Catholic and Anglican bishops to be rapidly ordained within Orthodoxy. However, this is a matter of oikonomia and not recognition of Apostolic Succession.