What is the purpose of keeping two days Yom Tov in the diaspora especially since we now know the exact times for Yom Tov, candle lighting etc.
Answer:
Although it is true that the purpose of the second day of Yom Tov is no longer relevant for today – the original purpose was on account of there not being sufficient time to inform the dwellers of distant places of the correct date for Yom Tov, and today, when we follow a fixed calendar, this is not longer relevant – we continue to observe the second day of Yom Tov, because this was a rabbinic enactment that we do not have the halachic authority to repeal.
See Rambam, Hilchos Mamrim, Chap. 2.
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