Metzger: A Textual Commentary on the Greek New Testament

The second edition of this companion to the Greek New Testament discusses textual variations based on the critical apparatus. It contains a thorough explanation of each textual decision that appears in UBS4. It was especially designed for translators who have not received formal training in textual criticism. It enables them, and other people interested in the initial text of the Greek New Testament, to discover more easily the reasons that certain variant readings in the NT are more likely to be original than others. An easy-to-read introduction provides a brief overview of textual criticism, including explanations of key terms, a history of the text, and methods that are used by scholars to arrive at their conclusions.

From the Introduction
“Most commentaries on the Bible seek to explain the meaning of words, phrases, and ideas of the scriptural text in their nearer and wider context; a textual commentary, however, is concerned with the prior question, What is the original text of the passage? That such a question must be asked – and answered! – before one explains the meaning of the text arises from two circumstances: (a) none of the original documents of the Bible is extant today, and (b) the existing copies differ from one another.”

A Textual Commentary on the Greek New Testament (2nd Edition)
A Companion Volume to the United Bible Societies’ Greek New Testament (4th Revised Edition)