Kindness sounds like the simplest thing in the world, and that is exactly the point. The poem is only three short lines, and it turns on a gap between speaking and living. "Kind" is a word a child can say without thinking. But the last line, "hard to be," admits that saying it and actually being it are very different things.
The speaker sounds quietly honest, maybe a little rueful. There is no lecture here and no scolding. The poem doesn't tell us to be kinder; it just points out how difficult kindness really is, and that feels like the speaker including themselves in that struggle. The title repeats the word, so we meet it twice, plain and unadorned, much like the language around it.
The mood is calm and reflective, with a small sting at the end. The short lines leave plenty of white space, which gives us a moment to pause and ask how often we manage to live up to a word we say so easily.