is an expression in Japanese used to highlight important information in a similar way to 'to sum up', 'in summary', or 'in short' in English. It is a combination of the する-Verb 要（よう） 'to need', or 'to require', and に. Literally it means something similar to 'as for what's necessary (A)'.
This is a phrase that will only ever take the initial position in a sentence, before expressing a condensed version of what has previously been said.
In short, this means that you lied on your resume, didn't you?
So, in summary, I can't eat any food that has wheat in it?
In short, I was being used by him.