Not sure where you heard that! St Mark the glorious saint is the author of the earliest Gospel to be written and it was written in KOINE GREEK mainly for the gentiles.
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None of the original works of the NT were written in any language but Hebrew.
Mark’s gospel may actually be the third to be written, but was definitely not the first.
By Paul’s testimony in his epistle to the Romans, “the Oracles of Yehova are committed to the House of Judah.” (not to the Helenists that had been driven out of the land in the Maccabee revolt, centuries before the era of Yeshua and his disciples)
Revisionism and general rejection of the Word of Yehova are the fare of the “critics” and the rest of the Adversary’s bride.
“Koine Greek” is an accidental creation of the Pharisee scribes that translated the Hebrew NT writings into ‘Greek.’ It was never a language spoken by any peoples. This is the opinion of actual native Greek scholars.
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