Everything that we understand we come to know through experience. There are two types of experience that can lead to understanding–direct experience, and belief in something that is conveyed to us symbolically.
Direct, pre-linguistic experience allows us to know things in a way that we often find difficult to convey or describe because language is a flawed tool. However, the use of language (defined broadly as any symbolic communication) is the only way in which we can convey the knowledge we have gained through direct experience to others.
Language involves the use of words, which we use to point at terms. Terms are the meaning which language approximates through the use of words. The use of language allows us to come to terms with another person–to understand one another and ensure that we are talking about the same thing when we use the same words.
The problem is that because words are symbols, they are not the thing itself. Our use of language runs ashore as we get deeper into the metaphysical weeds. The more fundamental and abstract the concepts become the more we see language fall short as a modality for both communicating our understanding to others, or coming closer to the truth through the use of language.