Filioque in the context of "East–West Schism"

Papal primacy, also known as the primacy of the bishop of Rome, is an ecclesiological doctrine in the Catholic Church concerning the respect and authority that is due to the pope from other bishops and their episcopal sees. While the doctrine is accepted at a fundamental level by both the Catholic Church (Eastern and Western) and the Eastern Orthodox Church, the two disagree on the nature of primacy.

English academic and Catholic priest Aidan Nichols wrote that "at root, only one issue of substance divides the Eastern Orthodox and the Catholic Churches, and that is the issue of the primacy." French Eastern Orthodox researcher Jean-Claude Larchet wrote that, together with the Filioque controversy, differences in interpretation of this doctrine have been and remain the primary causes of schism between the Catholic Church and the Eastern Orthodox Church. In the Eastern Orthodox churches, some understand the primacy of the bishop of Rome to be merely one of greater honour, regarding him as primus inter pares ("first among equals"), without effective power over other churches. A prominent 20th century Eastern Orthodox Christian theologian, Fr. Alexander Schmemann, envisioned a primacy that sums up rather than rules over: "Primacy is power, but as power it is not different from the power of a bishop in each church. It is not a higher power but indeed the same power, only expressed, manifested, and realized by one."

The Catholic Church and the Eastern Orthodox Church have been in a state of official schism from one another since the East–West Schism of 1054. This schism was caused by historical and linguistic differences, and the ensuing theological differences between the Western and Eastern churches.

The main theological differences with the Catholic Church are the papal primacy and the filioque clause. In spirituality, the tenability of neo-Palamism's essence-energy distinction and of the experiential vision of God as attained in theoria and theosis are actively debated.

The different Denominations of Christianity have variations in their teachings regarding the Holy Spirit.

A well-known example is the Filioque controversy, the debates centering on whether the Nicene Creed should state that the Spirit "proceeds from the Father" and then have a stop, as the creed was initially adopted in Greek (and followed thereafter by the Eastern Church), or should say "from the Father and the Son" as was later adopted in Latin and followed by the Western Church, "filioque" being "and the Son" in Latin.

Pope Sergius III (c. 860 − 14 April 911) was the bishop of Rome and nominal ruler of the Papal States from 29 January 904 to his death. He was pope during a period of violence and disorder in central Italy, when warring aristocratic factions sought to use the material and military resources of the papacy. At the behest of Theophylact I of Tusculum, Sergius seized the papal throne from Antipope Christopher, who in turn had deposed Pope Leo V. Sergius' reign was subsequently marked by Theophylact's influence. As pope, Sergius continued many ecclesiastical controversies of his predecessors, including conflict over Pope Formosus' legacy, annulling all ordinations made by the late pope, and the filioque controversy with eastern patriarchs. His pontificate was similarly marked by temporal conflicts, with Sergius' refusal to crown Berengar I of Italy as Holy Roman Emperor, and his support of Byzantine Emperor Leo VI the Wise's fourth marriage. Sergius also saw the restoration of the Lateran Palace.

Sergius III today is largely seen as an unscrupulous character as contemporary records had included a number of accusations against him; Sergius III had reputedly ordered the murder of his two immediate predecessors, Leo V and Christopher, and allegedly fathered an illegitimate son who later became pope, John XI. His pontificate has been variously described as "dismal and disgraceful", and "efficient and ruthless".