The elderly man went to see his priest. He told him that he had been living with a curse for the last 40 years and wondered if the priest could do anything about it. The priest said “Well, maybe. But I need to know the exact words of the curse.”

Without a pause the elderly man replied “I now pronounce you man and wife.”

and that would be to murder him, as a mercy killing.

 
He left out the words:   "...till death do you part."

 
Shortest sentence in the English language:   I am
Longest sentence in the English language:   I do.