Since ancient books were copied entirely by human scribes, mistakes were not uncommon. Throughout this codex, an ancient editor has made corrections to the scribe's original text. In some cases, this means adding a word that the scribe mistakenly omitted (example 1, where the word ἡμῶν has been added by the editor), or in other cases, emending a word that has been written incorrectly (example 2, where the corrector has placed an upsilon over an eta, effectively changing ἡμῶν into ὑμῶν).
Mistakes could occur for a number of reasons. Sometimes, the original text from which the scribe was copying might be itself incorrect. In other cases, the scribe might omit a word by losing his place in the text. Other errors arose from the scribe's own understanding of the text; a scribe might insert a synonym for a word or misspell a word based on his own pronunciation. Example 2 could be an instance of this second effect, since the vowels upsilon and eta were pronounced very similarly during the third century A.D.
Corrections could be made by an editor before the book was sold, or at a later time by the owner of the book. In ancient times, many variants of the same text were often in circulation, each with slightly different readings. Thus, it was not uncommon for the owner of the book to go through the text and correct the variant readings.
In the process of correcting a text, it was sometimes necessary to delete a letter, word, or phrase that had been written by the original scribe. In P46, the deletion was accomplished neatly by placing a dot over the letter(s) to be deleted. In example 3, above, the phrase τῷ ζῶντι has been deleted from the text. (The papyrus is rather worn at this point, so reading the letters may be difficult. However, the dots above the letters are visible.)