#1 New Moons and Sabbaths
The original Sabbath at creation did not have an evening and morning. The evening and morning Sabbaths were given to Israel as a sign to remember the original Sabbath given at creation. The text usually quoted to show that the evening and morning sabbath is not a symbol of he true sabbath, but is itself the true sabbath is Isaiah's reference to mankind bowing down to worship God from "one Sabbath to another". The argument goes that the Sabbath cannot be a symbol because it is being kept in the new heavens and the new earth. However if this is the case, the text also refers to the Jewish festival of the New Moon. The implication being that the New Moon festival is also something to be kept forever, and not simply as a sign of the truth.
The New Moon festival and the Sabbath were both held in high esteem in the Old Testament:
Num 10:10
"Also at your times of rejoicing - your appointed feasts and New Moon
festivals - you are to sound the trumpets over your burnt offerings and
fellowship offerings, and they will be a memorial for you before God."
Num 28:9-15
"On the Sabbath day, make an offering of two lambs a year old without
defect, together with its drink offering and a grain offering of two-tenths
of an ephah of fine flour mixed with oil. This is the burnt offering for
every Sabbath, in addition to the regular burnt offering and its drink
offering. On the first day of every month, present to the LORD a burnt
offering of two young bulls, one ram and seven male lambs a year old, all
without defect. With each bull there is to be a grain offering of
three-tenths of an ephah of fine flour mixed with oil; with the ram, a grain
offering of two tenths of an ephah of fine flour mixed with oil; and with
each lamb, a grain offering of a tenth of an aphah of fine flour mixed with
oil. This is for the burnt offering, a pleasing aroma, an offering made to
the LORD by fire. With each bull there is to be a drink offering of half a
hin of wine; with the ram, a third of a hin; and with each lamb, a fourth of
a hin. This is the monthly burnt offering to be made at each new moon during
the year. Besides the regular burnt offering with its drink offering, one
male goat is to be presented to the LORD as a sin offering.
1 Sam 20:5
"So David said, 'Look, tomorrow is the New Moon festival and I am supposed
to dine with the king."
2 Ki 4:22-23
"Please send me one of the servants and a donkey so that I can go to the man
of God quickly and return"
"Why go to him today?" he asked, "It's not the New Moon or the Sabbath."
Is 1:13-14
"New Moons, Sabbaths and convocations - I cannot bear your evil assemblies.
Your New Moon festivals and your appointed feasts my soul hates."
Ez 45:17
"It will be the duty of the prince to provide the burnt offerings, grain
offerings and drink offerings at the festivals, the New Moons and the
Sabbaths - at all the appointed feasts of the house of Israel".
Hos 2:11
"I will stop all her celebrations: her yearly festivals, her New Moons, her
Sabbath days - all her appointed feasts."
Amos 8:5
"saying 'when will the New Moon be over that we may sell grain, and the
Sabbath be ended that we may market wheat?'"
So clearly the reference to the "New Moon" in Isaiah was a reference to the New Moon festival of the Old Testament. This is not your understanding in your reply, as you argue "New Moons happen once a month and often connoted something important in the Jewish calendar. So it will be in the new earth" Clearly you are mistaken here - the New Moon is not simply a reference to the new moon, but to the New Moon festival. Therefore to claim that because Isaiah refers to the Sabbath being kept in the new earth this means the evening and morning Sabbath is not a sign you logically must also believe that the New Moon festival of the Old Testament also is of this nature. But as we can clearly see from the Old Testament references cited above, both the evening and morning Sabbath and the New Moon festival were an essential part of the whole Old Covenant. All Isaiah is saying is that the festivals of the Old Covenant will be kept in the New Earth.
This can be seen more clearly at the end of Ezekiel. In vision Ezekiel is shown a time in the future when the glory of God will return to the temple at Jerusalem "this is where I will live among the house of Israel for ever" (Ez 43:7). We then learn what it will be like when God lives with him people - the temple will be rebuilt, and - as in Isaiah - God's people will worship him on Sabbaths and New Moons. However these are very much in the style of the Old Covenant:
Ez 46:3
"On the Sabbaths and New Moons the people of the land are to worship in the
presence of the LORD at the entrance of that gateway. The burnt offering the
prince brings to the LORD on the Sabbath day is to be six male lambs and a
ram, all without defect. The grain offering given with the ram is to be an
ephah and the grain offering with the lambs is an is to be as much as he
pleases, along with a hin of oil for each ephah. On the day of the New Moon
he is to offer a young bull , six lambs and a ram, all without defect. He is
to provide as a grain offering one ephah with the bull, one ephah with the
ram, and with the lambs as much as he wants to give, along with a hin of oil
with each ephah."
Now Adventists don't keep the New Moon festival and they don't keep the other Old Testament festivals either. So the text from Isaiah proves more than the traditionalist Adventists want. It shows that Isaiah, like Ezekiel, believed the Jews would be celebrating all the Old Covenant festivals on the New Earth. Read Ezekiel 43-48 and Isaiah 60-66 to get the full picture.
Hope that has made things clearer for you.
John