To enter by reason means to realize the essence through instruction and to believe that all living things share the same true nature, which isn't apparent because it's shrouded by sensation and delusion.
To see nothing is to perceive the Way, and to understand nothing is to know the Dharma, because seeing is neither seeing nor not seeing and because understanding is neither understanding nor not understanding.
Whoever realizes that the six senses aren't real, that the five aggregates are fictions, that no such things can be located anywhere in the body, understands the language of Buddhas.