From The History of the Anti- Ecumenical Activity of the Church of Russia

The Assembly of the Heads and Representatives of the Orthodox Churches, also known as the All-Orthodox Council, took place in Moscow from June 8 to June 18, 1948. Officially, it was dedicated to the 500th anniversary of the autocephaly of the Russian Church. The Russian Church planned this celebration of its jubilee one month before the founding assembly of the World Council of Churches, a principal organ of the ecumenical movement, which all local Orthodox Churches were expected to join.
The Council was organized during a challenging political climate following World War II (1939-1945). The article discusses the conditions, essence, and purposes of the council, focusing on several questions: Did the Russian Church indeed have ambitions to invite the World Ecumenical Council? Was the council's resolution truly reflective of the independent stance of the Orthodox Churches? Was it initiated by the Soviet government or the Russian Church to fulfill far-reaching geopolitical ambitions using the church?
Sources confirm that the Soviet state attempted to use the church to satisfy its expansive foreign political ambitions; indeed, plans for a preliminary assembly of the World Ecumenical Council had been underway in Moscow in the late 1940s, alongside other issues of inviting the World Council.
However, the plan faced setbacks, which were exacerbated by the international situation, resulting in the refusal from parts of the autocephalous churches (Alexandria, Jerusalem, Cyprus) to participate in a preliminary council. The ecumenical movement rejected increasing the representation of the Russian Church in its governing body. As a result of these refusals, the Russian Church declined to join the World Council of Churches, a decision confirmed by the 1948 council's resolution.
The assembly was essentially a forum for exchanging views among representatives of the Orthodox Churches, conducted under strict control by the anti-religious Soviet regime. The assembly was subjected to participation by representatives of the churches of the countries controlled by the Soviet Union, under pressure from their secular leaders. Only the Church of Antioch was an exception.
The anti-ecumenical nature of the 1948 Moscow Assembly was conditioned by the global political climate but aligned with the interests of the Russian Church as well.