In Christian usage, terms such as 'baptism', 'church' or 'faith', whose roots go back to New Testament times, have a central meaning. The author uses Paul’s letters, i.e. the oldest New Testament writings, to determine the early use of such terms and examines them from a historical-semantic perspective. The focus is on the Pauline use of the term ›pistis‹, which is examined with regard to the question of the origin of a Christian language and classified in terms of linguistic history. This also includes the question of the appropriate understanding of the syntagma ›pistis Iesou Christou‹. While the current discourse is determined by the substantive alternatives Faith in Jesus Christ and Faith or trust in Jesus Christ in relation to God, this study develops a new solution on the basis of linguistic and idiomatic investigations.