Information is not only transmitted by words on the actual spoken language.
We all have and trust quite a lot other types of signs, like voice tone and gestures.
In fact, those transmit some kind of information that reaches your brain faster in a somewhat stronger way than actual word-based language.
The same as some random dog that doesn't understand much of your words but reacts to your voice tone and gestures, we can build empathy with some given character based on the voice acting (given proper characterisation).
Also, we can understand that something being said is straight, or irony, or sarcasm, or full of hate, etc. via voice tone and acting; much more than for the actual words.
THAT IS THE FUCKING IMPORTANCE OF VOICE ACTING.
Your senses trust more those signs than the words, specially in building empathy, sustaining suspension of disbelief, and believing the character personality.