You can make an invisible event with a show text command like, "I should listen to the chief's advice first before I go in there."
maybe followed by a move player event.
You can create another event page that requires a switch to be turned on after talking to the required NPC. Leave the second page blank so it does nothing and make sure to have it set to below character to let the player pass. The NPC event will also need to trigger a switch to be turned on of course.
If the passage is more than one tile wide, you can also copy and paste that event.