From the man who is said to have converted Justin Martyr
[the words of Christ] have in themselves something of dreadful majesty, and are enough to put to shame those that turn out of the right way, while rest most delightful comes to those who carry them out in practice
Truth carries forth, in the Church
Even Protestant scholars can agree that apostolic truth is maintained within the church into the post-apostolic age.
The Apostles' Creed then, in its present shape, is post-apostolic; but, in its contents and spirit, truly apostolic. It embodies the faith of the ante-Nicene church, and is the product of a secondary inspiration, like the Gloria in Excelsis and the Tedeum, which embody the devotions of the same age, and which likewise cannot be traced to an inidividual author or authors. It follows the historical order of revelation of the triune God, Father, Son, and Holy Spirit, beginning with the creation and ending with the resurrection and life eternal.The quote is taken from a section in which Schaff is defending the "rule of faith" by which spiritual truth is preserved over time by those of faith.
The Orthodox agree. The Orthodox hold that something like that "rule of faith" has consistently, through the power of the Holy Spirit, preserved truth to this very age, not just in matters of "core/essential" doctrines, but in matters of faith and practice for Christian living wholistically.