This is one of Browning's famous love sonnets that celebrates and extols the love that the speaker has with her beloved. The poem is built around a central image of the two souls of the speaker and her beloved standing together and close, "erect and strong," by themselves in the world and enjoying perfect unity on every level. This union is so perfect that the speaker says that if they desired to "mount higher" then the angels would spoil their union by dropping a "golden orb of perfect song / Into our deep, dear silence." Therefore, to avoid this disruption, the speaker tells her beloved that they should stay on earth:
--where the unfit,
Contrarious moods of men recoil away
And isolate pure spirits, and permit
A place to stand and love in for a day,
With darkness and the death-hour rounding it.
So, the poem ends with a recognition of how imperfect is. However, it is this very imperfection that makes it such an excellent place for the lovers to stay together, precisely because the "contrarious moods of men" automatically recoil from "pure spirits," isolating them together, and allowing them to be united, albeit temporarily, as the lovers are always reminded by the darkness and the threat of death.
This poem therefore seems to be a celebration of the love that we can enjoy here on earth, and whilst recognising that it can only be temporary, the poem acknowledges that there is a deep and profound joy to be had in making the most of such a love now.