What's the message of the poem?

Setting aside the ambiguity of the term “message,” the poem seems to discuss the contrasts between tradition and new thinking, between habit and modern adjustments to tradition. Frost, who was more interested in “sketches” of New England (both physical features and humanistic personality traits), was observing a seasonal ritual – two neighbors meeting for a mutual task, repairing a stone wall after a winter’s damage caused by swelling of frozen terrain – and the illogic of that tradition, because there was no actual pragmatic need for any fence at all at that particular boundary between properties. Frost’s conciliation of these two epistemologies (ways of knowing) takes the form of quoting (twice) a time-honored but seldom challenged homily: “Good fences make good neighbors.”

The friendly irony of the homily is that, while "good fences" may once have referred to avoiding disputes of property lines or trespassing of livestock, it now supports the social value of neighbors meeting at least once a year to renew their warm-hearted acquaintance, in this shared activity, an opportunity to talk while working, catching up on each other’s lives. Frost "sketches" another social trait of New Englanders, a quiet reserve of feelings, an abhorrence of nosiness, a value in privacy.