Answer: Message
Explanation:
According to elements of persuasion,message is described as central content that contains emotional as well as actual arguments. Message is written by the writer, therefore the complete control on message belongs to the writer.
According to the situation in question,Jeremy is in dilemma with message of the persuasion element. He is not able to decide whether the content of message should contain strong argument or surprise elements.
As he has total control over the message he can involve any element he want to convey through that message.