You don't realize how important momentum is until you lose it. I've written a lot about our loss of the mighty mo last year, and at the congregational meeting a couple of weeks ago I shared how we have regained it...spiritually, emotionally, numerically, etc.
Here's how it works: Momentum leads to Mobilization leads to Mission. You lose momentum, it effects the mission. That's not to say that God needs our momentum. God does his work and accomplishes his purposes...period. But our participation and joy is increased when we're in his stream. Losing mo is like sitting on the shore while watching the white water rafters shoot by, laughing (and screaming in fear) down the rapids. I prefer to be in the raft on the rapids.