"Do not abandon the commandments of the Lord, but keep what you have received, without adding or subtracting."
The Didache is one of the most important sources from the age of the Apostolic Fathers; so instrumental, in fact, that some of the early Fathers considered it to be a part of the New Testament.
Effectively the oldest extant written catechism, it provides both moral and liturgical instruction, including the oldest recorded Eucharistic prayers.
In a time characterized by ambiguity and evasiveness, the simplicity with which the Didache puts forward its teaching is itself an instruction.
Links
Mike Aquilina on the Didache: https://www.catholicculture.org/commentary/episode-6-whats-in-name-anonymous-texts-from-early-church/
Translation courtesy of Catholic University of America Press: https://www.hfsbooks.com/books/the-apostolic-fathers-walsh-grimm-marique/
Alternate Translation at CatholicCulture.org: https://www.catholicculture.org/culture/library/fathers/view.cfm?recnum=1631
Theme music: 2 Part Invention, composed by Mark Christopher Brandt, performed by Thomas Mirus. ©️2019 Heart of the Lion Publishing Co./BMI. All rights reserved.