Costers' work places her, like many of her fellow Augustinians, in the
devotio moderna ("modern devotion") movement, and she urges a "reformation of the spiritual life in her convent" and a stricter observance of the Augustinian rule. Her
Visioen en exempel was written in the style of the
Visio Tnugdali, a 12th-century religious text of otherworldly visions. Her patron saint was
John the Evangelist, and her
Previlesien van Sint Joannes Evangelist systematizes a set of devotions to him. Order and system were important to her, and she set up the devotions in a numerical structure similar to the
Rosetum by
Jan Mombaer, an Augustinian friar (1460–1501). She draws on the
Gospel of John, his
Epistles and
Revelation, and possibly the
Golden Legend; Wybren Scheepsma sees her
Previlesien as evidence of the importance of the
Golden Legend in the Windesheim congregation. She was said to have had an encounter with Christ who explained the "purpose of suffering", and in a letter described a revelation in which
Saint Anne appeared to her. ==References==