From 1957 to 1961, studied philosophy Kessler, Catholic and Protestant Theology at the Eberhard Karls University of Tübingen and Würzburg in the Julius-Maximilians-University. Between 1987 and 2003, Kessler was professor of systematic theology (dogmatic and fundamental theology) at the Johann Wolfgang Goethe-Universität Frankfurt am Main._x000D_
Kessler is married and has one son.