What literary element is used in: "face to face for the last time in history with something commensurate to his capacity for wonder?"

In this final passages of the last chapter, Nick creates a parallel between Gatsby's dream and the dream of America. Gatsby failed to relive the past. In the end, even his idealism could not save him, nor change things in reality. For Gatsby, this was his "American Dream." Fitzgerald is making a critique with this story about the inability to achieve the American Dream. 

Nick reflects upon the old America, that land that early explorers...

In this final passages of the last chapter, Nick creates a parallel between Gatsby's dream and the dream of America. Gatsby failed to relive the past. In the end, even his idealism could not save him, nor change things in reality. For Gatsby, this was his "American Dream." Fitzgerald is making a critique with this story about the inability to achieve the American Dream. 

Nick reflects upon the old America, that land that early explorers would have seen when they first came to this New World. The New World was full of promise and wonder. Over time, the land was developed and "America" evolved into something else, something with less wonder and promise. Similar to how Gatsby's dream began in hopeful idealism and ended in tragedy, Nick seems to suggest that the hopeful idealism of America in its beginnings has also become corrupted. Something has been lost. 

Nick says that man (meaning humanity) was "face to face with for the last time in history with something commensurate to his capacity for wonder." This is quite a statement. He means that when (any) man looked at the New World (America before it was America) that would have been the last time anything lived up to humanity's greatest amount of wonder. The notion is that America could never again live up to this high esteem, with its having fallen like Gatsby's original idealism. Given that this is such a dramatic statement, we could call it hyperbole, a literary element in which something is exaggerated to make a dramatic point. There is also a use of personification in that man is face to face with the New World. The New World is given a "face," a human quality, in order to give America a character or personality. And this character is marked by idealistic hope, optimism, and wonder. One might even call this a kind of flashback because, even though he was not there, Nick recalls America in its inception.