Looking through the rules there are rules for discarding down to the maximum hand size of five cards. I can't see any time when you put cards in your hand. Cards are always placed in the sanctum. It is noted that the sanctum can hold any number of spells and items.
I was super confused by this as well. I can only think that previously the rules were draw a card to your hand. When you start to work on it put it in your sanctum but they changed it and forgot to take the rule out.