They were selected as an essence or Kernspruch ("text-kernel") of the verses in question, with the intention of highlighting dramatically or summarising in a terse fashion a significant thought from the Gospels.
The latter came to predominate by the end of the 16th century due to the emphasis placed by the Reformation on the need to make the Bible accessible to all people through the use of the vernacular language.
[3] During the late 16th and early 17th centuries a number of composers drew on Gospel readings for an entire church year's worth of Sundays and feast days to create complete cycles of motets.
[5] The genre fell out of general fashion by the early 18th century but was still in demand for use in funerals, as evidenced by the composition of motets by Johann Sebastian Bach for such ceremonies.
[6] Bach wrote for the function of enhancing the prescribed gospel reading several cycles of cantatas for all occasions of the liturgical year.