Cleansing, like you said, is washing away impurities, like washing veggies for dinner sort of only in a magical sense. Purifying is more prepping something for work. To stick to kitchen analogies, it’s kinda like popping a roast in the oven for dinner. Personally, and ritual work is largely a personal thing, for cleansing I use things like salt, sage, my besom, and make a point of removing energies I don’t want hanging around, whereas with purifying, rather than sweeping energies away and just scaring them off, I tend to sort of…. I’m not quite sure how to word it to make sense, but ‘push in the light’ I guess. Again, like cooking a roast, you aren’t taking cold out, but putting heat in. Hope that makes some iota of sense.