Tomorrow night is a new year. Tomorrow night all of the energy allotted to the universe for the past year will have been spent and the world will be a sapped and hollow shell.
In order for G-d to invest another year's worth of energy into this project called creation, He will have to be extremely motivated. He must be overcome with passion. What elicits G-d's desire to create?
The prospect of union, of an intimate bond with His other half.
If we tell G-d that we want to have a committed and exclusive relationship with Him for another year, then He's willing to create the world in which that can happen.
Rosh HaShanah is not so complicated. It's a simple day on which we are asked a simple yes-or-no question. "Are you in or are you out?"
If we say "in" then G-d's passion to create is ignited. The ball is in our court. We know what G-d is hoping for. He's waiting for our answer.
Rosh HaShannah is the day on which the Infinte reveals His vulnerability -- the romantic hope for a blissful union with His people, Israel.