[2] After several positions as chaplain, Kempf became the parish priest of the Church of the Heilig Geist in Riederwald, part of Frankfurt, from 1942 to 1949.

[2] On 25 July 1949, Kempf was consecrated as Bishop of Limburg, succeeding Ferdinand Dirichs who had died in a car accident.

[5] As bishop, Kempf contended with the aftermath of the war, including the rebuilding of damaged churches, integration of displaced persons (Heimatvertriebene), and establishment of new parishes in the major cities of Frankfurt and Wiesbaden.

[3] He promoted spiritual discourse and open dialogue ("geistige Auseinandersetzung und offenen Dialog), introduced liturgical reform, and a structure in which priest and lay people cooperated.

[2] The central meeting house of the diocese of Limburg in Wiesbaden-Naurod, which he had planned as a place of spiritual intercourse and open dialogue, is named after him.