Tl;dr Early contact, close proximity to Judea, elements of class struggle, political flex to stay independent from Parthian empire are all reasons for why Christianity succeeded, which is seen as a contingent but retroactively necessary event. (I mention the Armenian Empire in 1 B.C., Armenians in Judea, Jews in Armenia, Armenia as a buffer state and haven for Christian refugees, the battle with the pagan religion, Gregory the Illuminator and more.)

Armenian from LA here, wonderful question really, which has fascinated me. Namely, how did St. Paul's call of "there is neither Jew or Greek, we are all equal in Christ" receive its first echo in Armenia, something which historian Nina Garsoian describes as "probably the most crucial step in [Armenia’s] history."

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My cynical, funny answer is along the lines of Armenian envy. Like, Armenians were jealous with the whole "chosen people" thing and said, "why not us also?" Thus, they invented Christendom.

Or, imagine the apostles Thaddeus and Bartholomew arriving in Armenia to preach the gospel, and a persecuting Armenian official, upon learning that the Garden of Eden and Noah's Ark are in Armenia, being absolutely thrilled with this new religion.

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More seriously, the question of Armenia's conversion has led me to grapple with my more liberal tendencies, such as the separation of Church and State. What does it mean, if anything, to be the first state to adopt Christianity as its official religion?

There are historical, geographic, socio-economic, and political reasons for why the Caucasus Christianized first, and I will focus primarily on Armenia (I will provide a speculative, philosophical conclusion).

Historically, recall that a century before Christ, Armenia was an empire that stretched all the way from the Caspian Sea down to the Mediterranean, Syria and Judea. The first cultural exchange occurred during this time, with Armenians in Judea and Jewish communities brought to Armenia by King Tigranes. During and after the time of Christ, there was an Armenian presence in the Holy Land. Regular pilgrimages to Jerusalem led to the formation of an early Armenian quarter there, which quaintly still exists in the old city alongside the three Abrahamic faiths (I say quaintly because, as a national quarter, it doesn't seem to belong next to religions; should it not be included as part of the Christian quarter? In reality it owes its current form to Ottoman-era nationality policies, as well as historic waves of continued settlement there, most recently settled by refugees from the Armenian genocide).

According to Dr. Roberta Ervine, the Roman military barracks in Jerusalem at the time corresponded with the location of the then-developing Armenian quarter. Moreover, many of the Roman soldiers that crucified Christ are written to have been from the Caucasus areas. Famously, the soldier to pierce Jesus’ side was of Georgian origin. So it is quite natural to think that pagan Armenians and peoples of the Caucasus were not only present in Jerusalem in and around the time of Jesus, but may also have witnessed the events and returned home with their testimonies.

Geographically, Armenia is pretty close to Judea. Close proximity allowed two of Jesus' apostles to preach there, according to Armenian tradition, which is why the Armenian Church claims apostolic origin. According to There were two routes of entry of Christianity into Armenia, one from Cappadocia and another from the south near Syria and Mesopotamia. Each route consequently brought with it a different strain of Christianity, namely a more hierarchic Greco-Roman form from the West and a decentralized, democratic version based on communal philosophy from the south. It was the western form that prevailed in the capital and spread outward establishing ecclesiastical hegemony.

Southwest of Armenia, the Kingdom of Edessa boasts earlier contact and conversion as mentioned. King Abgar of Edessa famously corresponded with Jesus according to church historian Eusebius. Armenian tradition (according to Moses of Chorene) claims King Abgar of Edessa was Armenian, but modern scholars assign him a Nabataean Arab origin. Nonetheless, many Armenians did settle and live in Edessa and Osroene, and certainly had contact with Christianity and helped spread it to Armenia.

The socio-economic reasons are also fascinating. According to this article from worldhistory.org titled The Early Christianization of Armenia, Christianity's entry into Armenia came with a powerful element of class struggle and also royal intrigues. “The end of the ancient pagan religion was a fine excuse to confiscate the old temple treasuries which were jealously guarded by a hereditary class of priests.”

Gregory used two powerful tools to spread the word: education and military power. Schools were established in which children of the existing pagan priestly class were prepared for the Christian priesthood. Meanwhile, military units were dispatched to destroy pagan temple sites and confiscate their vast riches, which were then used to fund Christian building projects. Naturally, many temple sites, along with several rich and semi-independent feudal principalities, resisted the new policy and these were put to the sword. Pagan traditions were never fully eradicated but they certainly became weakened by the removal of the temples and their economic resources. Still, many anti-Christian and pro-Persian aristocratic families persisted in resisting at least into the next century.

Christianity also outlawed “problematic” pagan practices, such as polygamy, incest, and dangerous pagan burial practices. The church established hospitals, hostels and orphanages. Armenia’s position as a trade route between east and west also facilitated contacts. The first martyrs of the Armenian church were queen Sanatruk and the Oskeanq and Sukiasianq, all of whom were ethnic Alans from the North Caucasus. Not only this, there are other hints of the multicultural framework of Armenia during this period. There were several Jewish communities in Armenia in the major cities of Tigranakert, Artashat, Vagharshapat and Zarehavan, which provided fertile grounds for the first proselytizers. Church historian Tertullian in 197 AD lists the Armenians as among the people who had converted to Christianity. And all of the 3rd-century Armenian monarchs are listed as having persecuted Christians, which suggests they were starting to become a problem.

Politically, Christianity allowed the monarchy to justify its rule through divine right. It primarily allowed Armenia to stay independent from the Parthian empire, which followed Zoroastrianism; it was also beneficial to Parthia’s rival Rome that Armenia should resist Persian influence and be part of the Roman sphere even if independent. Armenian independence would in principle not last long, as Armenia was split in 387 between the two powers and the Arsacid dynasty was formally deposed in 428. (Independence lay dormant until 885, granted by the muslim Abbasid Caliphate.) Still, in 405 Armenia invented its own alphabet with royal funding for the purpose of translating the Bible into Armenian; what followed was the Golden Age of Armenian literature, with the translation of important foreign texts into Armenian. Then, in a battle with the Persians in 451, Armenia was defeated militarily but allowed to continue practicing Christianity. Both of these 5th-century events are instrumental features of modern Armenian identity construction, as they are seen has having helped form and preserve Armenian identity as distinct from Persian and later Islamic influence.