The very first lecture of "Nietzsche's Zarathustra," not Nietzsche's "Thus Spoke Zarathustra," but the Princeton University Press book titled Nietzsche's Zarathustra, goes into discussing this to quite some detail, showing you how the ideas crept in, and the style of propaganda used then at the time to turn the Values of the ancient Greek on their head. The whole book is worth you time, even though it's completely off topic.

The New Testament is Written in Greek because the Old Testament was Helenized with Plato's Teachings by Philo Judeas. "Christianity is Platonism for the people." (Nietzsche, Prologue to Beyond Good and Evil) If you want, I'll PM you some little known history, direct from the source snips from a book vetted by Princeton.