I think that the primary message behind the poem is how people respond to grief. In the horrific nature of the accident it seems very surprising to find that the family returns to their normalcy so quickly. In the middle of the poem, the description of the boy, his pleading to not "Let them take my hand," the "spilling" of "life," and then the pulse indicating that the life was gone are all very intense and very sad. Yet, this is undercut with the ending as the family goes about their business because "they were not the one dead." In the end, perhaps the message of the poem is that, as individuals, we are captivated and held by tragedy that is reported, but this is temporary as we go about our business and understanding once we realize that we "were not the one dead." The discussion of tragic conditions and people's passing response to them could constitute a major message of the poem.
To me, the main message of this poem is that things happen just because of fate or chance or whatever. And these things totally change people's lives.
Think about what happens in this poem. The boy dies because of the accident with the saw. Nothing really caused it, it just happened. The saw leaped "or seemed to leap" just because.
The other thing that makes this so random was that they decided to keep working when it was already late. If they had stopped working (it was already getting dark) then the boy would have lived. Or maybe his sister distracted him by saying "dinner." Who knows?
So the main idea is that chance or fate has a big impact on our lives.
The key to understanding the theme of Frost's "Out, out-" lies in the intertextual reference to Shakespeare's "Macbeth" Act V Sc.5, where Macbeth soliloquizes bitterly on the futility of life after he learns of the death of his wife:
Out, out, brief candle!
Life's but a walking shadow, a poor player,
That struts and frets his hour upon the stage,
And then is heard no more. It is a tale
Told by an idiot, full of sound and fury,
Frost's poem ironically comments on the death of a small boy who dies tragically at such a young age because of an accident when he was sawing wood. His life is compared to a "brief candle." Frost's message is that anything can happen at any time. There is no absolute safety or security for human life. The next minute is not ours and we may be alive one minute and dead the very next minute. The only thing that we can do is to go on with our lives. Just because the small boy died it does not mean that all the others will die in a similar fashion. The death of the small boy cannot be an excuse for inaction. So, the others continue with their work and lives even after the death of the boy:
No one believed. They listened at his heart. Little--less--nothing!--and that ended it. No more to build on there. And they, since they Were not the one dead, turned to their affairs.
The buzz saw is the bitter device that is set against the beauty of the smell of cut wood. Frost uses the poem "Out-Out" to describe the accident. He seems to be trying to make some sense of the accident. The boy is doing his chores and cutting the wood when the saw slips from his hands. The boy is working like an adult and relates to his own death like an adult. He is surprised when the accident occurs and realizes that death is to follow. The poet can find no reason for such an event. The tasks and time was an ordinary day with ordinary things going on. The girl even calls the boy to supper. In the end after the boy has died despite the doctor's attempts to help him the family turns away to go on living.
"No more to build on there”
The boy is gone from them.