Craft refers to the mechanics of fiction: plot, characterization, dialogue, pacing, flow, scene-crafting, dramatic structure, point-of-view, etc. I think craft is pretty easy to teach and it’s easy to learn. It’s technique, the foundation upon which writers use their artistic skill to build their story. Knowing the mechanics of craft enables you to use it to create the effect you want.
Story refers to the page-turning factor: how compelling is your story, how unique or original, does it connect with the reader, is there that certain spark that makes it jump off the page? Is it sufficiently suspenseful or romantic (as appropriate)? Does it open with a scene that intrigues and makes the reader want to know more? Story comes from the imagination of the writer and is much more difficult to teach than craft (if it can be taught at all).
Voice is the expression of you on the page—your originality and the courage to express it. Voice is what you develop when you practice what we talked about yesterday—writing what you know. It’s the unfettered, non-derivative, unique conglomeration of your thoughts, feelings, passions, dreams, beliefs, fears and attitudes, coming through in every word you write.