This may seem to be an unlikely selection, but hear me out.
Gronkowski's performance will be vital to the Patriots' success on a number of fronts: (1) pass protection/run blocking, (2) safety-valve receptions and (3) production in the red zone.
In terms of blocking, Gronkowski will be crucial in helping the Patriots establish a strong ground presence early on in the game. If he can consistently get into or past the second level of the Dolphins defense, RBs Green-Ellis and Danny Woodhead should be able to consistently rip off strong gains. In addition to run blocking, Gronkowski will likely be asked to provide chip blocking on blitzing downs, thereby allowing Brady the time he needs to make a play.
On the subject of passing downs, Gronkowski will be expected to be Brady's safety valve on most plays. Should the Dolphins double-cover WRs Deion Branch, Wes Welker and Chad Ochocinco, Brady will look to dump the ball off to Gronkowski. If "Gronk" is able to make those catches and turn upfield, he'll force the Dolphins to play him tighter, thereby freeing up other offensive weapons.
Finally, and most importantly, Gronkowski will be asked to help the Patriots turn red-zone opportunities into touchdowns. During the second half of the season in 2010, Gronk produced seven TDs in red-zone situations. If he can continue that type of production during this season, the Patriots will be well on their way to another division title.