Charles Ellicott Commentary Isaiah 66:23

"And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith Jehovah." — Isaiah 66:23 (ASV)

From one new moon to another ... — Under the Mosaic law, Israelites were bound, at least in theory, to attend the temple at the three great feasts. In the new Jerusalem, as the prophet thought of it, the pilgrimages would be both more frequent and more universal. Every Sabbath and new moon would witness not Israel only, but all flesh, thronging into the courts of the temple. It is in the very nature of these words that they never have received, and never can receive, a literal fulfillment. The true realization is found in the new Jerusalem of Revelation 21:22-27, of the perpetual sabbatism of Hebrews 4:9, and even that glorious vision is but the symbol of spiritual realities.