we have all heard sabbathists argue endlessly for years.
literally no one here has never been confronted with such talk before.
therefore a more needful thing, if you actually believe Isaiah in the way you claim to, is this -
are you going to make a 'you must observe the new moon festival' thread?
or do you just throw this verse out there thoughtlessly?
Isaiah is cited in the context of the New Heavens and new earth, and I even said that is why it was cited. Isaiah shows the monthly meeting and weekly meeting to worship God in the New Heavens and new earth. The Sabbath, the seventh day rest of God did not end with Calvary AD 31.
You ask about the New Moon. Good question.
Isaiah 66's context of new heavens and new earth, and the month therein is found in Ezekiel and Revelation.
Ezek 47:12: "And by the river upon the bank thereof, on this side and on that side, shall grow all trees for meat, whose leaf shall not fade, neither shall the fruit thereof be consumed: it shall bring forth new fruit according to his months, because their waters they issued out of the sanctuary: and the fruit thereof shall be for meat, and the leaf thereof for medicine."
Rev 2:7: "He that hath an ear, let him hear what the Spirit saith unto the churches; To him that overcometh will I give to eat of the tree of life, which is in the midst of the paradise of God."
Rev 22:2: "In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations."
Rev 22:14: "Blessed are they that do his commandments, that they may have right to the tree of life, and may enter in through the gates into the city."
The New moons reveal that event to come. Since AD 31, and fulfillment of Passover to Pentecost, moons were still counted, but not as type, but antitype, from the 3rd month (Sivan) when Pentecost occured, Acts 2:1-4,18-19,33; Psalms 133:1-3; 1 Peter 1:12; Revelation 5:6, unto the antitypical month of Ethanim (1 Kings 8:2), which was anti-typically "five months" (Revelation 9:5,6,10), in AD 1833/4, which tied into the stars falling as Revelation 6:13, which was 40 years after the beginning of 1793 (start of the 3 1/2 day/years of Revelation 11:9,11, unto AD 1797/8 the end of the 3 1/2 day years and end of the 1,260 and 1,290 of Daniel & Revelation), and ten years before the 50th year and anti-typical Jubilee of AD 1843/4 (end of the 2,300 and 1,335 of Daniel & Revelation, see Dan. 8:13-14,26; Rev. 9:13-15).
We are anti-typically in the 7th month still, nearing the close of the Anti-typical Day of Atonement, as seen in Leviticus 16 & 23; Revelation 20 at least.
The Next New Moon anti-typically will be after the anti-typical 7th month is over, after the final anti-typical feast of Tabernacles takes place.
Rev 7:9: "After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;"
See also end of Rev. 14.
Thus the next New Moon anti-/typically takes place as Isaiah said, New Heavens and New Earth with the tree of life once again there in Eden restored, the first dominion.
The 7th day is not a type of shadow, since God's law is light (Proverbs 6:23). The 7th day, the Sabbath of the LORD is an eternal memorial (Remember, Exodus 20:8).
Thank you for your question, as it gives me opportunity to lay out the scriptures (truth; John 17:17) of the matter for all to see and test by those scriptures.