Probably the most obvious reason why the Western church, has done more missionary activity than the Eastern churches throughout history is numbers. As of 2018 statistics, in the West, the Roman Catholic Church has 1.3 billion adherents worldwide and the Anglicans and Protestants number 900 million. By comparison, the Eastern Catholic Church has 18 million members worldwide and the Orthodox Churches have 280 million members worldwide. Looking at those numbers we can understand why more missionary activity took place in the Western church, since there is strength in numbers.
We also must consider factors such as the political situation and the socioeconomic factors that the people faced. In many Eastern European countries the common folk lived in oppressive circumstances, of being serfs to foreign landowners, or being under atheistic regimes that did not tolerant any form of religious identity or expression. For most, faith was an important part of their daily lives, but so was survival, so the thought of putting time and energy into expanding beyond their worldview, which was usually their village and church was not possible.
Another reason is that in the Eastern Churches have another ethos or understanding of what mission means. “Western Christian churches have “done mission” on a large scale (especially in the last two centuries), but the forms of mission used by Western Christians have never been part of the experience of Orthodox Christian churches. Therefore, though the 1990s saw the restoration of Orthodox churches’ ecclesiastical and spiritual life, there was not a corresponding resurgence of their mission. For an Orthodox Christian the word “mission” sounds strange, even unknown; the closest equivalent is “witness”—that is, believers bearing witness to Christ and his Good News among other nations and peoples.” (Christian Mission in Eastern Europe, Valentin Kozhuharov, April 2013, www.internationalbulletin.org)
For the Eastern Churches, the majority of missionary work or witnessing to the faith has taken place within ethnic and national boundaries. As a result the expression of their Eastern Christianity whether Eastern Catholic or Orthodox has been linked with their cultural identity, which is beautiful and meaningful to those people, but when that same Eastern Catholic or Orthodox expression of faith is transplanted into to a new land such as Australia, Brazil, Canada, the United States etc. the cultural identity can at times appear as a barrier for others to feel welcome and desire to join that Church.
“In recent centuries, Eastern Christianity has been very lax in the field of evangelization. We have rightly focused on serving the needs of our people, but sometimes to the exclusion of spreading the Gospel to those who have not heard it. Historically, this has not always been the case. In the ninth century, SS. Cyril and Methodius conducted a successful mission to the Slavs, under the patronage of St. Photius the Great. And in the nineteenth century the Russian Orthodox mission to Alaska bore great fruit. It is unfortunate that the missionary imperative seems to have fallen on the back burner since then.
The most compelling reason to evangelize is to fulfill Jesus” command:
And Jesus came and said to them, “All authority in heaven and on earth has been given to me. Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. (A Practical Guide to Evangelization for Byzantine Catholic Parishes by Anthony T. Dragani, www.east2west.org)
Whether you call it mission, witness or evangelization, we are called as Eastern Catholics, Western Catholics and/ or Orthodox to spread the Good News to everyone, regardless of race, colour, ethnicity, nationality or language. Christ came to save all of us, so that where He is, we too may be. Regardless of what was done in the past we are to embrace the present and share the Good News of the Gospel with everyone we encounter.