What does Sarty think when he sees the house of Major de Spain? Why does the house make him feel safe?

Sarty's reaction contributes to the work as a whole in
several ways.  It provides unity when Sarty compares the house to a courthouse,
referring backward and pointing forward to the courthouse scenes.  It also reveals where
Sarty's mind is, figuratively:  on the courthouse.  His reaction also emphasizes the
hopelessness and poignancy (a quality of specialness) of and in Sarty's
position:  essentially, his reaction is mostly one of relief--this house, these people,
are too big to be hurt by his father, Sarty thinks.  He is only a wasp to them.  The
house is beyond Abner, Sarty thinks.  He is relieved:

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...They are safe from him.  People
whose lives are a part of this peace and dignity are beyond his touch, he no more to
them than a buzzing wasp:  capable of stinging for a little moment but that's all; the
spell of this peace and dignity rendering even the barns and stable and cribs which
belong to it impervious to the puny flames he might contrive...this, the
peace and joy, ebbing for an instant as he looked again at the stiff black back, the
stiff and implacable limp of the figure which was not dwarfed by the house, for the
reason that it had never looked big anywhere and which now, against the serene columned
backdrop, had more than ever that imperious quality of something cut ruthlessly
from tin,...

Sarty's reaction
also, then, renews the image of Abner as metal, as tin, without heat (visible anger),
but hard like tin. 

Sarty's reaction also provides
foreshadowing, of course, since Sarty will end up being wrong--not even this house and
family and barn are beyond Abner's reach to maintain his dignity in his warped
way.