For the good of the country, Brendon McCullum must open the batting in test matches because, if he doesn't, there is no room for Luke Ronchi - and that would be a crying shame.
Kane Williamson, Ross Taylor, Dean Brownlie, BJ Watling and McCullum would make up three through seven, so there is no room for Ronchi. Four bowlers are needed because no one in the top seven bowls well enough to play as the fourth bowler.
Could Ronchi displace one of those players? In time, maybe, but right now it would be unfair because none of those players deserves to be dropped just yet. In fact, the one under most pressure is surely McCullum and let's face it he is not set for the chop. In fairness he is a good enough player to be allowed to ride out a form slump.
But here's my point. Right now Luke Ronchi is the best first-class batsman currently playing Plunket Shield.
Forget his T20 efforts, this bloke is churning them out in the longer form. So far in the Plunket Shield, Ronchi has scored 760 runs at an average of 69 with four centuries. Therefore McCullum, as captain, has to think of his team before himself and open. That allows Ronchi to move into the top seven. New Zealand simply can't afford to enter a test environment without their best available batsmen.