The diagonal lemma as the formalized Grelling paradox
  Since the diagonal lemma plays a key role in the proof of the main limitative theorems of logic, its proof could shed light on the very essence of these fundamental theorems. Yet the lemma is often characterized as one of those important logical results that lack an insightful explanatory proof. By making explicit that the well-known proof of the lemma is just a straightforward translation of the Grelling paradox into first-order arithmetic, the proof can be made completely transparent. 
Gyorgy Sereny