The correct answer to this open question is the following.
What is this quote saying simply is that language and thought are the elements that mostly distinguish humans from animals on planet earth.
Is the person saying that humans are being called animals?
No, that is not the case. It could be interpreted that way but if we closely pay attention to the words expressed by the author, we can say that it finds many similitudes between humans and animals. However, the biggest differences are language, our capability to speak, and of course, our ability to use the mind, the reason to think
That is why the author says that "There is no mode of action, no form of emotion, that we do not share with the lower animals. It is only by language that we rise above them, or above each other - by language, which is the parent, and not the child, of thought."