During different periods of history, the Ecumenical Church has faced various problems of doctrinal, administrative and organisational natures, solutions to which have been provided during the Ecumenical Councils. One of such councils was the Second Ecumenical Council, convened upon the order of the King Theodosios in Constantinople, in 381.
As the result of Arian disputes, a new heresy had appeared, the head and supporter of which was Bishop Makedon of Constantinople, who denied the deity of the Holy Spirit. The Ecumenical Council convened in Constantinople on that special occasion, re-endorsed the definition of the Ecumenical Council of Nicaea and the concept of “One deity, three persons”.
Accepting the Ecumenical Council, the Armenian Apostolic Church commemorates the memory of 150 Patriarchs participating in the Council.