The speaker argues that love should never be a matter of convenience. If it is, it becomes a kind of betrayal, "high treason" against what love ought to be. The second stanza makes the point sharper: convenient love is like a peace signed on bad terms, a truce that only papers over break-up and feud rather than settling anything.
The poem then narrows to a single room, which it calls "the last enemy to all the world." The image suggests a small, closed-off space where two people shut out everything else, and the poem seems wary of that retreat. Falling "from time into desire" has a dizzy, weightless feel, as if desire pulls us out of ordinary life. The final lines say that nothing with real force or consequence, not even a hand or a wing, should be squeezed into "such a hole."
The mood is stern and a little cold, more argument than confession. The speaker sounds guarded, even scornful, of love that settles for small and easy.