Vast as was his distinctly medical work, Dr. Kerr was above all things a missionary. He never lost an opportunity to preach Christ. Kindly, just, dignified in his manner, he was always at work doing good and commending Christ to the Chinese.... He was a missionary first, and all his medical knowledge was used to commend the Gospel.
In 1890 he was a founding member of the Permanent Committee for the Promotion of Anti-Opium Societies. Fellow committee members were prominent missionaries BC Atterbury MD, American Presbyterian Mission in Peking, Archdeacon Arthur Evans Moule, Church Missionary Society in Shanghai, Henry Whitney MD, American Board of Commissioners for foreign Missions in Foochow, the Rev Samuel Clarke, China Inland Mission in Kweiyang; the Rev Arthur Gostick Shorrock, English Baptist Mission in Taiyuan and the Rev Griffith John, London Mission Society in Hankow. They resolved to continue their opposition to the opium traffic, urging Christians in China to arouse public opinion against it. The desire of the missionaries that their ideas be carried out caused them to form “continuation committees” that were assigned tasks to assure that action would be taken on whatever matters had been approved by the conferences.