The trial displays the clash of cultures that underscores the British presence in India.
Leading into the trial, there had been a clear division of cultures between India and the British. This division represents a clash because neither side is able to fully view the other in a open and transparent light. The Indians are resentful of the British presence in India. For their part, the British see the Indians as "backwards" and "savages." The dismissive attitude that both groups of people have towards the other makes consensus very difficult, if not impossible.
This cultural reality is present in the trial. What Dr. Aziz stands accused of confirms the very worst of British attitudes towards the Indians. For their part, the Indians see the trial as a perversion of British justice. The see the weight of institutional bias and discrimination hurled upon Aziz. Neither side is really paying attention to the crime at hand. Rather, it is an instant for one side to claim validation at the cost of the other. The trial characterizes the relationship between the two nations because each side refuses to see the other's frame of reference.
The trial does not resolve anything. If anything, each side hardens in its dislike of the other. This might be Forster's ultimate statement on how the trial characterizes the relationship between the two nations. Until there is an acceptance of the other, Forster might be suggesting that there will always be a cultural roadblock between both nations.