| Quote #4
Gregor […] complimented himself instead on the precaution that he had adopted on his business trips, of locking all the doors during the night even at home. (1.7)
Gregor's habits on the road become part of his everyday life. Locking up his room in his own house suggests that he feels his home to be just as unhomely as a hotel.
| Quote #5
Well, leaving out the fact that the doors were locked, should he really call for help? In spite of all his miseries, he could not repress a smile at this thought. (1.14)
Even though Gregor hasn't shown off his new body to anybody yet, he already feels more isolated. He's already aware, for example, of the effect that his transformation will have on everybody. He's still able to find some humor in the idea here, though, in contrast to his dejection in Part 3.
| Quote #6
But still, the others now believed that there was something the matter with him and were ready to help him […] He felt integrated into human society once again and hoped for marvelous, amazing feats from both the doctor and the locksmith, without really distinguishing sharply between them. (1.23)
Before he encounters anybody in Part 1, Gregor can still cling to the hope that he's part of "human society," and thus can be helped or cured by other human beings.