The answer of that question might be :
From the beginning of the novel, we can observe that the circumstances led Dr. Aziz and Mrs. Moore to meet each other. They met for the first time at the mosque .After some misunderstandings they became friends. She respected his religious character. He respected her because she appreciated his Muslim traditions.
We can also observe Dr. Aziz's good treatment to Mr. Fielding and soon they become great friends. Dr. Aziz had very good relationships with Mrs. Moore, Miss. Adela and Mr. Fielding .However the incident of the Caves had made great changes to the whole group. Miss. Adela has accused Dr. Aziz of trying to assault her. Dr. Aziz comes to hate her, because, for him, this accusation is worse than death. He is not afraid of the imprisonment, but he is certainly worried at his fair name suddenly having been tarnished by this scandal. As for Mrs. Moore, her experience at the Caves has ruined her interest and faith in humanity. Although she professes her belief in Aziz's innocence, she does nothing to help him. She died in her way back to England . And Dr. Aziz was highly respectful toward her and he was very sad when he heard of her death.
Moreover this accusation provides the opportunity for the friendship of Dr. Aziz and Mr. Fielding to be put to a test. This accusation makes them draw closer to one another, and secures the friendship between them. Fielding chooses to be in the side of his dear friend, Aziz, rather than with Adela.