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When performing new activities, people usually ask for detailed instructions to do things properly. The need is real, but it doesn't mean that satisfying it is the best thing to do.
If your goal is swimming, understanding the theory in advance won't help much. It could make things worse: more concepts with no connection yet with the actual feelings - can you explain being underwater to someone who's never been underwater? - will pile up in your brain, waiting for an explanation. The more concepts piled up, the messier their understanding would be.
Moreover, especially in a new, possibly uncomfortable situation like the awkward kickoff of a workshop, people will try to fit in, mirroring what seems to be the proper behaviour in the current situation. If one person asks for clarification about a detail, another might think, "Ok, it's question time now." ...and start asking another one. Suddenly, you're surrounded by a little crowd asking questions that can't be easily explained before the action.
Have people touch the problem first. Provide only the basic information needed to have them try, and clarify only in response to specific questions.
Do not create a "big theory" in advance: leave time to explain the whys later, after people have had the time and feedback to create a more solid mental model.
Provide safety : most participants can be first-timers, and out of their comfort zone. Clarify that we aren't expecting perfection, but that we'll progressively get there.
(Reading Pragmatic Thinking and Learning from Andy Hunt was a big eye-opener. A more thorough approach to the matter can be found in Training from the Back of the Room by Sharon L. Bowman.)
It is funny to see how the very same words slip away from the listener's mind when told before the experience, and stick instead once the experience forms an incomplete model with compelling questions.
However, if the questions are not about the workshop format, but on the political reasons to call the workshop, make sure you have collected everybody's expectations with an Expectations map