x x x x.
It is important to understand that the Apostolic Nuncio is the personal representative of the Pope. Therefore the key qualification, apart from competence in canon law, is that the person who is appointed Apostolic Nuncio must have the full confidence of the Pope.
Technically, an Apostolic Nuncio or an Apostolic Delegate is not
the personal representative of the Pope.
He is a permanent diplomatic representative (head of diplomatic mission) of the Holy See to a state or international organization (e.g., the Arab League), having the rank of an ambassador extraordinary and plenipotentiary, usually with the ecclesiastical rank of titular archbishop.
By international comity and convention, the Holy See is considered a state and is a member of the United Nations. International relations and diplomacy are conducted between and among states not between or among heads of states.