The speaker imagines a being so different from us that it shares no family tree with anything on Earth. Words like "parallel line that never intersects" borrow from geometry to capture that total separation. The poem even wonders whether such a creature would have ancestors at all, and jokes lightly that it might arrive in the world by something "less messy than sex." That small touch of humor brings the idea down to a human, slightly rueful level.
The turn comes in the last stanzas. "We probe the earth / & sky for you" suggests a collective search, perhaps scientific, perhaps simply longing. Then the speaker names what this stranger might be: a "cure for loneliness." The paradox is that the thing is "too other to be other," so strange that ordinary ideas of difference break down. The mood is quiet, curious, and a little wistful. The search for the unknown seems to come from a very human need for company.