Both "Tuft of a Flower" and "Reluctance" by Robert Frost deal with the theme that nature unites mankind.
In "Tuft of a Flower," the voice of the poem begins by lamenting that he had missed the grass mower, wanting to work alongside him as the voice of the poem turns the grass. The voice laments that "[he] must be, as [the mower] had been,--alone" (line 8). But then the voice sees a butterfly who lands on a "tuft of flowers beside a brook" (22). The voice of the poem had noticed before that butterflies were attracted to the flowers and was very happy to see that the mower had also loved the flowers and the butterflies and left the flowers intact. The voice then realizes that the butterfly has acted as a medium, binding the speaker's spirit with the spirit of the mower. This is the case because both the speaker and the mower love both the butterflies and the flowers, as we see in the lines:
The butterfly and I had lit upon,
Nevertheless, a message from the dawn,
That made me hear the wakening birds around,
And hear his long scythe whispering to the ground,
And feel a spirit kindred to my own. (31-36)
Hence, we see that their mutual love for the butterflies and the flowers is binding their spirits together, despite the fact that the mower is no longer present. In addition, now that the speaker has had that revelation, he no longer feels that he is working alone, but now rather feels united through nature.
Similarly, the speaker in "Reluctance" laments that he has wandered far from home only to return to see that the season has changed, that it is now autumn, and that all of the nature surrounding his home is dead. By the end of the poem, the speaker comments that it is treasonous for man to drift along through life, paying attention to his own reason, and accepting the end of seasons, rather than lamenting that the beauty is gone and that he has missed it. In addition, since the poem is arguing that all mankind should pay attention and respect to nature and the world around him, the poem is also showing us that nature binds mankind, just like the first poem.