I have all the thematic names and the instruction from the down clues. After a great deal of Googling I think I have four names (of which only three are needed). I cannot see these names anywhere in the grid. The instruction from the across clues makes sense up to a point (four words) and then I cannot understand it (although it makes English sense) . I do have nine redundant words in the across clues, although the last three relate to clues whose answers involve part of the thematic names.
As I have absolutely no interest in the general theme, I suspect that I shall fail to see the 'cross' and the 'decisive event'. When I saw the puzzle I at once interpreted the title in what seems to be a productive way, but staring at the grid I am still lost. How annoying to be able to do all the crossword solving bit and then fail because I am not interested in the theme.