We seem to have no language, you and I; Our words are clothed in silence: not a sigh From lips encased in virtues smile; not a cry Lest ears not tuned to love, defile The sanctuary of that smothered breath, Where hope meets Death.
Two people, "you and I," find that they can't talk to each other. The speaker doesn't mean they're short of words so much as unable to use them: their words are "clothed in silence," dressed up and hidden. There is no sigh, no cry, only lips held in a polite, virtuous smile.
What stops them is fear. The speaker worries that "ears not tuned to love" might spoil something delicate, which the poem calls a "sanctuary" and a "smothered breath." That breath seems to be whatever feeling still exists between the two, and it is being kept alive only by being kept quiet. The final line, "Where hope meets Death," is blunt and short, and it leaves the poem on a note of ending. The title, "Finis," Latin for "the end," points the same way.
The mood is hushed, restrained, and quietly sad. Nothing is shouted, and that restraint is exactly what the poem is about: a feeling so guarded that it suffocates.