Theissen defines religion as a cultural sign language which corresponds to an ultimate reality and promise of a gain in life (p 324), a definition he expands on (pp 2-7). It is a semiotic, an objective sign system, making the world a habitable home that is then interpreted.
This interpretation of the world around us utilizes myth (explain what fundamentally determines history; in the Bible it’s the myth, the narrative, of the fundamental acts of G-d, rites (patterns of behaviour in order to depict what is happening in the myths; the first Christians developed a religious sign system without temple, without sacrifice, without priests), ethics (examine how the emphasis on Torah (law) continues in the Christian story).
Religion, a sign language, also has a systematic character, giving expression, eg to the denominational emphases (whether there is an altar, what is ‘on’ the altar). When the religion gives way to another how do these changing signs reflect faithfulness to the original story (eg eating meat sacrificed to idols)? And religious signs are a cultural phenomenon, produced by human beings, eg the theory of Christianity will be influenced by change. Intriguingly, such changes are brought about by charismatics, independently of pre-existing authority roles and traditions.
The two basic values of the primitive Christian ethics are love of neighbour and renunciation of status. Theissen details how these two values change from one religion (Judaism) to another (Christian), and then in Christianity from the synoptics to the Paulines, eg the Incarnation ‘is an expression of the greatest renunciation of status conceivable’ (p 78). Myth and ethic flow together: in the Philippians poem, G-d came in the flesh and provides the impetus for ethics.
Theissen develops powerfully the relationship of the changing values in the story of the church.