If the New Testament was first written in Aramaic language, then why (Western) Biblical scholars believe that the New Testament was originally written in Greek?
The influence of Jerome’s Latin Vulgate in Western Christianity.
For over a thousand years (c. AD 400–1530), the Vulgate was the definitive edition of the most influential text in Western European society. Indeed, for most Western Christians, it was the only version of the Holy Bible they ever encountered. The Vulgate’s influence throughout the Middle Ages and the Renaissance into the Early Modern Period is even greater than that of the King James Version in English; for Christians during these times the phraseology and wording of the Vulgate permeated all areas of the culture. Aside from its use in prayer, liturgy and private study, the Vulgate served as inspiration for ecclesiastical art and architecture, hymns, countless paintings, and popular mystery plays.
Influence of the Latin Vulgate on the English language
The Vulgate had a large influence on the development of the English language, especially in matters of religion. Many Latin words were taken from the Vulgate into English nearly unchanged in meaning or spelling: creatio (e.g. Genesis 1:1), salvatio (e.g. Isa 37:32), justificatio (e.g. Rom 4:25), testamentum (e.g. Mat 26:28), sanctificatio (1 Cor 1:30), regeneratio (Mat 19:28), and raptura (from a noun form of the verb rapiemur in 1 Thes 4:17). The word “publican” comes from the Latin publicanus (e.g., Mt 10:3), and the phrase “far be it” is a translation of the Latin expression absit (e.g., Mat 16:22 in the King James Bible). Other examples include apostolus, ecclesia, evangelium, Pascha, and angelus.
Jerome’s preface to the Latin version of the New Testament explains why for more than one thousand years, Christians in the West have mistaken the Greek New Testament for the original.
I am now speaking of the New Testament. This was undoubtedly composed in Greek, with the exception of the work of Matthew the Apostle, who was the first to commit to writing the Gospel of Christ, and who published his work in Judæa in Hebrew characters.