Thoreau cuts past the sentimental notion that friendship thrives on compliments or reassuring talk—he's saying the real currency between friends is *understanding*, the unspoken recognition of who someone actually is. Two people can exchange pleasant conversation all evening and remain strangers; two others might sit in silence and feel entirely known. When your friend remembers how you take your coffee, or notices you're quiet because you're worried rather than bored, they're speaking the language Thoreau means—attention becomes eloquence. This matters because it frees us from the burden of always saying the right thing; sometimes the deepest friendship is simply being witnessed by someone who bothers to look.