LP+mingle

MINGLE : to become mixed, blended, or united. (dictionary.com [search mingle])

 "The fountains //mingle // with the river and the rivers with the ocean, the winds of Heaven mix for ever with a sweet emotion; "

This poem is about how seemingly everything else in the world is in love or together except for these two people and how the narrator wants to be with the person he/she loves. I think the author used the word mingle because it means to be united, and the narrator if this poem wants to be united with the person they love.

"In one spirit meet and //mingle// - Why not I with thine? "

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This line is used at the end of the end of the first stanza. Its saying how everything else is meeting and mingling with another, why not I with you? I think its also showing how the narrator feels about the separation between him/her and the person he/she loves. ======

Maybe the speaker offers such daunting subjects for mingling (oceans, mountains, winds, etc) so that the idea of the two of them mingling isn't as scary.