The idea that we cannot know the day and hour of the Lord's return seems to be a fairly common one in mainstream Christianity due to a number of verses. For example, one is Matthew 24:36 and another is Matthew 25:13.
Now, in recent times, there seem to be a number of suggestions out there that ...
@JonEricson I've looked at that question a few times and not been sure what to do. I don't know the Christian texts well enough to know what traditions y'all have about the day of return, and just answering the "how is RH calculated" part isn't on-topic here. Maybe if it were recast as "given these texts (quote), when is the day of return" would be a better fit?
@JonEricson not in the sense of "end times". Rosh Hashana is the day of judgement; it's an annual event, part of a period of self-examination, repentance, making amends, forgiveness. The text doesn't tell us how to compute days beyond "new moon"; the business of eyewitness testimony and the court declaring is the rabbinic implementation. They also calculated the date and that's what we do now. (IIUC, even when they still did it with witnesses, they calculated as sort of a checksum.)
So if the Christian sources say that the day of return can't be known and that it will be on Rosh Hashana, then it can only be unknown if it's the year and not the day that's in question.
@JonEricson if not, that's why we have revision histories. :-)
BTW, I'm speculating on shofar for that particular assembly, but the prophetic texts that talk about moshiach might actually say something. That exercise might call for a concordance (or online search).
A shofar () is a horn, traditionally that of a ram, used for Jewish religious purposes. Shofar-blowing is incorporated in synagogue services on Rosh Hashanah and Yom Kippur.
Shofar come in a variety of sizes.
Bible and rabbinic literature
The shofar is mentioned frequently in the Hebrew Bible, the Talmud and rabbinic literature. The blast of a shofar emanating from the thick cloud on Mount Sinai made the Israelites tremble in awe (Exodus 19:16).
The shofar was used to announce holidays (Ps. lxxxi. 4), and the Jubilee year (Lev. 25:9). The first day of the seventh month (Tishri) is ...
At any rate, I re-wrote the question. Not sure if I can venture an answer, however.