I think that "to clarity" should be "to clarify." In the passage, "to clarity" makes no sense, but "to clarify" would mean:
"Here is what I'm saying in simple terms: it may be necessary to advertise...."
"To the astonishment" means "to my (or someone else's) surprise." Example:
"I did the mashed-potatoes (a dance) to the astonishment of the audience."