Theodor Undereyck was a Protestant pastor, spiritual writer and pioneer of pietism in the German Reformed Church.
Background
Theodor Undereyck was born in 1635 as the son of businessman Gerhard Undereyck and his wife Sara, née Salanger. After the death of his parents in 1636 by the plague, he grew up as an orphan in the house of his uncle Johann Undereyck in Alstaden.
Career
In particular Cocceius strongly influenced him in the direction of a federally theological thought, so that he was also considered one of the "big catechists of Coccejanismus". Voetius influenced him in the direction of a puritanical way of life and its emphasis on the importance of Christian conventicles. From 1658 to 1659 Undereyck undertook a study trip to Switzerland, France, and England.
In 1660, he became pastor of the Reformed church in Mülheim an der Ruhr.
There he led approximately 1661 one of the first Pietist conventicles in Germany. In 1670 he became pastor primarius in the community of Saint Martini in Bremen and remained so until his death.
Undereyck published 5 books, including two catechisms and a lay dogmatics, in which he conveyed the ideas of the English and Dutch Reformed theology to German-speaking readers in edifying language.