Dear Mr and Mrs Smith,
Thank you for inviting us to your wedding. It was an unparalleled experience.
The cashier at the church was a very innovative way to finance the event. I am certain I would be unable to equal such an ingenious move. In fact my fiancee told me so in no uncertain terms, and she made a point adding how awestruck she was at seeing him again at the reception later.
It was most thoughtful of you to inform us where we could buy the food to bring -- otherwise we would have been late to the party itself.
All of this has made us understand how insufficient in comparison our wedding would be. We don't wish to inflict such a paltry experience on the two of you. I apologize for sending you the invitation earlier and hope you are gracious enough to forgive us for not retracting it sooner than we did.