As the historian Jacques Monet observed,
"[A] king is a king, not because he is rich and powerful, not because he is a successful politician, not because he belongs to a particular creed or to a national group. He is King because he is born. And in choosing to leave the selection of their head of state to this most common denominator in the world- the accident of birth- [people] implicitly proclaim their faith in human equality; their hope for the triumph of nature over political manoeuvre, over social and financial interest; for the victory of the human person".
This is true for New Zealand as well. We accept a hereditary head of state because every other method of choosing one has proven to be undesirable. Hereditary appointment is a neutral way to select a head of state. It ensures that he or she will be above partisan politics and that the head of state will have the best interests of the whole nation at heart, not just the interests of those who elected or appointed him or her. No elected official could ever claim to represent an entire nation because he or she owes their position to only those who voted in their favour.
Monarchs are born to their job and have no say in the matter; they would even need parliament's approval to relinquish it. The price of being a King or Queen is a lifetime of service. They do not retire at the age of 65, but work until the day they die. The Queen knew this when, on her 21st birthday, she said, "I declare before you all that my whole life, whether it be long or short, shall be devoted to your service…" No politician could or would ever make a similar claim.
Monarchs are trained their entire lives to do their job well. They have learned by watching their predecessors, and come to the job with more knowledge than any newly-elected official could. After years of service they accumulate vast experience and can offer that experience to elected leaders. Queen Elizabeth has been Queen longer than many of her Prime Ministers have been alive.
New Zealand has a long history of great monarchs who have carried out their jobs far better than most presidents anywhere in the world. A hereditary monarch brings many benefits to our system of government. Combined with an elected Prime Minister, it is the best political system ever invented.