Contradiction with Romans 14:5
This verse suggests that individual believers can esteem one day above another or consider every day alike, which conflicts with the regular worship practice indicated in Isaiah 66:23.
Romans 14:5: One man esteemeth one day above another: another esteemeth every day [alike]. Let every man be fully persuaded in his own mind. [fully persuaded: or, fully assured]
Contradiction with Colossians 2:16-17
These verses indicate that nobody should judge others regarding a holy day, contrasting with the implied regular observance in Isaiah 66:23.
Colossians 2:16-17: Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath [days]: [in meat...: or, for eating and drinking] [respect: or, part]
Contradiction with Galatians 4:9-10
These verses criticize returning to weak and beggarly elements, including observing days and months, which contradicts the ongoing observance suggested in Isaiah 66:23.
Galatians 4:9-10: But now, after that ye have known God, or rather are known of God, how turn ye again to the weak and beggarly elements, whereunto ye desire again to be in bondage? [turn ye again: or, turn ye back] [elements: or, rudiments]
Paradox #1
Some people find the idea of worshiping God on both new moons and Sabbaths, as suggested in Isaiah 66:23, inconsistent with other biblical teachings that focus primarily on the Sabbath as the main day of worship. In the rest of the Bible, the Sabbath is often given special importance, so including new moons might seem different from the usual emphasis.