This page is a “stub”: a placeholder, so I can link to it, while I have not yet finished writing it. The text that follows, if any, is an explanation of what the page will say, rather than the proper contents of the page itself.
According to dualist eternalism, monism is wrong because it is not possible to achieve union with God.
If it were possible, the core logic of dualist eternalism—sin and salvation—would fail.
This critique is decreasingly effective, because more and more people reject the authority of the established (dualist) religions, and see no argument that unity with God is impossible, beyond “priests say so.”
For further reading, before I write this section: the Vatican has published, online, a very nicely done criticism of the New Age, much of which applies to monism more generally. (The New Age is pervasively monist.)