Mac just updated to MAC OS Mojave 10.14.2 now pages won't work

Pages v7.3 is a different application and document format than experienced with Pages '09. As Pages v7.3 still does not implement all, or implement identically, features found in Pages '09, some documents may not open with the same appearance as they did in the older application. Any attempt to change any content in an opened Pages '09 document will cause a dialog asking if you want to convert to the new document format. Once you do that, it won't be a Pages '09 document any longer.

If you have the retail iWork '09 DVD, and keep a copy of the iWork 9.3 Update (has Pages v4.3 in it), then you have the basis to install the iWork '09 applications on an older implementation of macOS, or OS X. Do to the nature of its installation into System locations, just dragging Pages '09 v4.3 to the Trash will not fully uninstall it.

What specific version of pages when you select the Applications : Pages.app icon and press command+I (get info)

If it is Pages '09 v4 (purple ink bottle) then it is broken with no ability to open or create new documents, and no fix.

Otherwise, what in an explanatory context does “pages won't work” mean?

LIke I said, Pages '09 v4.3 is a cooked goose on Mojave. There is no update for it as it was retired in 2013. There is Pages v7.3, which will open Pages '09 documents, but it is not Pages '09 v4.3 by a long shot.