Is Noah's arc meant to be a true story for christians?
It isn't intended to be a true story for Jews so why would it be meant to be true for Christians? Rabbi Hillel, one of the most revered rabbis of all time who lived in the first century CE, has a very famous quote about the Torah.
1. Most famous perhaps is the incident which occurred before his rise to leadership, when he was not yet a scholar, but had a burning desire to study Torah. At that time, Torah study was tightly controlled and limited only to those of the highest caliber and to those who could pay for it. Hillel, working then as a woodchopper, did not have enough money to pay for entry into the Beit Midrash. On a freezing cold snowy day, he climbed onto the roof of the Study Hall, and lay at the "skylight" listening to the lecture, until he froze. When the scholars below observed his form above, they retrieved him, and changed the policy such that anyone who wished to study Torah could come in and do so.
2. A certain non-Jewish "wise-guy" came to scoff at the Torah, first to the home of Shammai, then to the home of Hillel. He said, "Teach me the Torah while I am standing on one foot." Shammai, sensing his true intention, had him thrown out forthwith. (From this story, probably mostly, Shammai has received the bad "rep" of being a short-tempered, person who "did not suffer fools" lightly. However, this is certainly not the case, since it is Shammai himself who teaches "Receive everyone with a smiling face.")
When the individual came to the home of Hillel with the same request, Hillel responded. "No problem! The main idea of the Torah is 'Love your neighbor as yourself.' Everything else is commentary. Now, if you're really interested, go and study the commentary." So impressed with Hillel's response, according to Jewish Tradition, was the visitor, that he took Hillel up on his instructions, began to study the Torah seriously, and became a Jew. Source
Matthew 7:12 says basically the same thing.
So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets. NIV
One message in both religions. Be right with God; be right with your brother (we are all brothers). The rest is commentary.