The question of the original language of the Gospels is by no means of minor significance, nor does its importance lie simply in the correct understanding of single passages. The answer carries with it the atmosphere in which these writings were produced, their antecedents, and, to a considerable extent, their immediate purpose. The problem of dating them is also involved, and thus the history of the earliest Christian tradition.
The external evidence is practically zero. There is the oft-quoted statement attributed to Papias of Hierapolis in Phrygia (early second century): Matqai/oj me'n ou=n ebraidi diale,ktw ta, lo,,gia ounegra,yato that is, Matthew wrote his Gospel (that, apparently, is what "Logia" means) in Aramaic. But neither the source of this information, nor the context in which it stands, can inspire confidence in its value. Nor is there any other statement regarding the composition either of this Gospel or of any of its fellows, which appears to be based on genuine tradition. Schmiedel's conclusion seems fully justified: "All that can be said to be certain is this, that it is in vain to look to the church fathers for trustworthy information on the subject of the origin of the Gospels."
Before considering further the literary material, certain more general questions must be touched upon. The fact that every known text of the Gospels is Greek, or derived from the Greek, has from the first given very strong support to the belief that these writings emanated from a church which had already cut loose from the Jews. This conclusion has two corollaries: the comparatively late date of even the earliest Gospel (Mark), and the necessity of regarding Greek as the original language of the evangelistic tradition.
The underlying belief, however natural and seemingly necessary, finds no support in the writings themselves. Each of the four is plainly written, at least primarily, for Jewish readers; no one of them steps out of the atmosphere of Palestine even for a moment. (The Gospel of Luke is no exception; though it is dedicated to a Gentile reader, its material is wholly Palestinian and of early date.) The argument is addressed to the chosen people, and the good news for the Gentile world is given less space, and less emphasis, than it has in the O. T. prophets, who had provided all that was necessary. Incidental declarations, such as Mt. 10:6, 23(!), Mk. 7:27, Lk. 19:9 f., 22:30, 24:47. Jn. 4:42. are very significant. There is nowhere any suggestion that the center of gravity of the new Messianic faith might be moved beyond the boundary of the holy land. Jn. 12:20 ff. provided the perfect opportunity, but the idea was not there. Each of the Gospels has its parenthetical explanation of Semitic words and Jewish customs, for the benefit of Gentiles readers; all these are provided by the Greek translators. The one fundamental aim of the four evangelists was to demonstrate that Jesus of Nazareth was the Messiah of the Hebrew scriptures, the divine-human being foretold in the Prophets and the Psalms.
from pages 253- 255, The Four Gospels