Two short lines, and nearly all the feeling sits in the first word: "if." The speaker has something huge to say to another person, maybe love, grief, regret, or just everything they've been carrying, but can't find language big enough or exact enough to say it. The poem doesn't tell us what "everything" is, and that's part of its power. We're left to fill it in ourselves.
The mood is quiet and a little aching. There's tenderness in the way the speaker addresses "you" directly, as if the wish to be understood is real and close. But there's also frustration, even helplessness, in the idea that feeling can outrun speech. The lowercase "i" and the plain, simple wording make the speaker seem small and unguarded, someone not performing but admitting something. Ironically, the poem is itself a few words trying to point at a much larger silence. It suggests that what goes unsaid can matter as much as what is spoken.