The meaning of the novel's ending is that friendship between Aziz and Fielding is not possible at this time in Indian history.
The opening of the last chapter features Aziz and Fielding believing that they are "friends again." They start off on their horse ride with the idea that their friendship can resume. However, as they start taking, the social and political issues of the day cause friction between them.
Fielding wants to understand more of the spiritual dimensions of India. He sees the attraction it holds to Ralph and Stella and is intrigued with it himself. However, this is not something that appeals to Aziz because Fielding is seeing it from a Hindu point of view. Aziz is Muslim. His spiritual value system is different than what Fielding is seeking.
As their conversation continues, they move to the subject of India under British Rule. Fielding has changed a bit from his original stance. He now embraces the idea that India would fall apart if the British left. In a version of the “England holds India for her good" that he used to reject, Fielding's views are different from Aziz's. Dr. Aziz believes that India needs to be free from the British. He goes as far as saying that either in his generation or his children's, the British will leave. Since both men believe in opposite visions, another level of difference results.
Aziz and Fielding do not outwardly reject one another's friendship. However, Forster suggests that given the condition of India at the time, their friendship is not going to happen. Fielding is different. Aziz is different. Both have become more polarized. This means that they view their side as the "right" side. Neither of them speaks with a tolerant and accepting attitude toward the other.
Forster suggests that friendship cannot live in a such a setting. Friendship is not possible across a racial or national divide when people are unwilling to show flexibility in their beliefs.