After he finished school, Arnold studied education, philosophy, and theology in Breslau, Halle, and Erlangen. He engaged in Christian youth work and in evangelism among the poor through the Salvation Army. While in Halle, he became part of the "German Student Christian Movement", and its General Secretary. In 1907 he and his wife von Hollander seceded from the Eva state church "Evangelische Kirche". His work with the Salvation Army increased his sympathy for the oppressed classes of people and strengthened his stand for preaching conversion and salvation. Here in Halle, he also met Emmy von Hollander and married her in 1909.