More than fifteen years ago, studying the book on my own in the summer after my first year of seminary, I read the following footnote in the second volume of Robert Jenson’s Systematic Theology (p. 257n.48):

Is a Eucharist celebrated by an unordained person really the Eucharist? The question is perhaps unanswerable. Something happens, and we cannot know what, in the mercy of God, that may be. But the event should not have happened; a “valid” Eucharist it certainly is not.

It took a long time for me to understand the import of the question, as well as how—considered in the light of the church’s long history, traditional teaching, and liturgical practice even across divided communions—decidedly representative it is and not parochial, bizarre, or idiosyncratic.