The apostle has been telling his followers that they need to be taking off two days for the Feast of Trumpets. The reasoning behind that is that if the new moon is not sighted on the scheduled day, that it will happen on the next day and since you will already have it off, you will be safe in God's sight and not horribly embarrassed.
He also is trying to wean is followers away from resort Feast sites because of all the temptation to stray from God's path during those eight days. There too, he is encouraging an extra day to be added on to the Feast. Your boss is really going to love that!
The seventh month begins with the NM which is also a High Day. When the NM is seen that High Day begins, not before. The concept is simple: If it doesn’t happen today, it will happen tomorrow!
It is only prudent to take two days off work to avoid any embarrassment, just in case Trumpets is not on the day calculated; that does NOT mean that Trumpets is two days as teh Rabbins say. trumpets is only One day!
There is then plenty of time to set the other Festival dates; an din any case there would at the max be only a one day difference between calculated and observed and in the vast majority of case the NM would be seen as calculated.
The real issue is around today’s resort non Feasts which are vacations with the excuse of a biblical Feast. If we all camped on a local farm and met in the barn and truly kept the Feast rejoicing together; what would it matter if we stayed a day beyond what we calculated?
Today people rush home, even travelling on the Eighth Day; what a shame! I would expect that if someone declared the feasts not necessary a very large number would not attend. Most people are doing what they are told and not because they love pleasing God, or because these festival messages are so inspiring. James