What does the father gain from this experience with the boy?In the answer, please consider the father's treatment of his son.

It is interesting that Hemingway chooses the father,
rather than the mother as the observer of his child; also, it is rather curious--if not
unnatural--that the mother does not become involved in the situation involved in the
short story "A Day's Wait." 

Be that as it may, the
father's initial close observation of the boy's condition seems incongruous to his lack
of anxiety about his son's illness when he says, "I'll see you when I'm dressed." Here
the reader may well wonder if Schatz has had the flu before. Then, when the doctor is
called and he explains to the father (still no mother in the scene!) that "there was no
danger if you avoided pneumonia," the narrative seems more
realistic.

Nevertheless, the father fails to sense the
magnitude of his illness for the boy when he tells him,"...you don't have to stay if
it's going to bother you."  For, the father simply feels that the boy is worried about
his contracting the flu germs.  Instead, however, the boy speaks of what he believes is
his approaching death.

Because of the father's lack of
intuition and perception, Schatz faces alone the greatest of existential crises: the
possibility of death.  Schatz bravely "holds" himself against nothingness in a
conflict marked by his sense of terrible aloneness.  And, when the father finally
comprehends the struggle of his boy, he speaks to him as though he is merely a fellow
soldier, "Poor old Schatz....." only consoling him logically. Perhaps, Hemingway wishes
to convey that this struggle with nothingness is, ultimately, one that man must endure
alone.

Finally, it is a detached narrator/father who
observes that his son's "gaze" at death relaxes, but he "cried very easily at little
things that were of no importance."  This emotional response of Schatz to little things
indicates the trauma that the boy has suffered, his release of his courageous
attitude, yet the father offers no physical or emotional comfort to his son.  This lack
of reaction on the part of the father suggests the point of view that each person must
face alone existential issues.