One of the main principles that Gandhi followed, and which has made him famous in history is his defense of non-violence. Gandhi believed that it was possible for people to change their political and social reality through peaceful methods.
This speech is likely to appeal to the viceroy because the viceroy was most likely concerned about violence or conflict between English and Indian people. As India moved towards its goal of independence, the British government was likely to be concerned with the possibility of violence, and thus was reassured when the violence was condemned by an important Indian character.