In Christian language usage, terms such as "baptism", "church" or "belief" are of central significance. They go back to the days of the New Testament. On the basis of the Pauline Letters, i.e. the oldest of the New Testament scriptures, the author identifies the usage of such terms and examines them from an historical semantic perspective. He thereby focuses on the Pauline use of the term 'pistis' and its derivatives, which he examines and classifies etymologically with respect to the question of the emergence of a 'Christian language', including the question of an adequate understanding of the syntagm 'pistis Iesou Christou'. While the current discourse is determined by the alternative meanings 'belief in Jesus Christ' and 'belief of Jesus Christ', this study proposes a new solution on the basis of etymological and idiomatic analyses.