The main problem confronting the editor of the New Testament is demonstrably as old as the oldest surviving New Testament documents. The problem is, quite simply, to find the best way of displaying known differences. . . . What is important to recognize is that the modern reader, puzzled by the details of a critical apparatus, is in the same position as the ancient reader of P66 [2nd/3rd century Gospels on papyrus]: one is confronted by variant forms of the text.

D. C. Parker, An Introduction to the New Testament Manuscripts and Their Texts, 191.