"That's the message I will be delivering to the team today, that it is a big game, in front of 30,000 hopefully in Auckland in a finals scenario, which is pretty exciting."
There will be many in the crowd interested to see Jesse Ryder back. It's safe to assume he will play given he was added to the squad on Monday after scoring a pile of runs in domestic cricket, but it's debatable whether he does it as an opener.
Martin Guptill and Rob Nicol have given New Zealand good starts at the top of the order and McCullum saw little need to alter things. Ryder would likely slot in anywhere from No 4 to No 6, depending on the situation, and provide extra stability with Ross Taylor still out.
The 27-year-old arrived at New Zealand training today minus some of the extra padding around his midrift after reportedly following a new diet and fitness regime. Ryder hasn't always been the model professional but has missed playing for the Black Caps as he works his way back from his latest injury.
"I don't really care about his weight," McCullum said. "That's irrelevant to me. It's whether he's capable of scoring runs and contributing to the team in an attitudinal manner as well. When Jesse is going well, he slips into this team brilliantly. He works incredibly hard.
"He's obviously had his issues over the years but, hopefully, there's been some distance been put between those incidences. Jesse is a class player. When he's on song, he strengthens our team. That's all I'm worried about."
Ryder isn't the only selection dilemma, and Doug Bracewell might not survive the cut. The allrounder has come in for some treatment in the shorter forms of the game throughout the summer - Richard Levi was particularly severe on Sunday as Bracewell went for 37 runs from two overs.
It would be a bittersweet couple of days for Bracewell considering this morning he won the best test bowling performance award at the fifth annual ESPNcricinfo Awards for his 6-40 in New Zealand's defeat of Australia in Hobart.
Bracewell wasn't the only one who came in for some treatment from Levi, who smacked 117 not out from just 51 balls.
New Zealand aren't getting too hung up about Levi's innings - "I think it was probably a guy at his absolute best," McCullum said - but they had looked at their areas to bowl to the Proteas opener and had get-out areas square of the wicket at Eden Park.
There were no plans, however, to let up in the banter department.
Tim Southee, in particular, mouthed off even as Levi was in full stride but New Zealand are mindful of the fact South Africa haven't always coped when the stakes are high.
The stakes aren't massive tomorrow night but the match will set the tone for the rest of the series.