Like vcsjones says, the solution here is git checkout:
git checkout <refspec> -- path/to/directory # or path/to/file
where <refspec> can, for instance, be HEAD, that is, the current working commit. Note that this usage of the checkout command will affect the working tree but not the index.
git revert is used to “revert a commit”, and by this, it should not be understood that the commit disappears from the tree (it would play havoc with history — if you want that, look at git rebase -i). A reverted commit consists of applying, in reverse, all changes from the commit given as an argument to the tree and create a new commit with the changes (with a default commit message, which you can modify).