© David M. Howard, Jr.
An expanded version of this essay appeared as "Evaluating Commentaries on Joshua," The Southern Baptist Journal of Theology 2.3 (Fall 1998): 4-10.
In its most basic sense, a commentary simply makes comments on a text. In the best commentaries, these comments are not random or impressionistic statements that may or may not have a legitimate connection with the meaning of the text at hands. Rather, they focus on the text, and on making the text's meaning more clear.
Commentaries do this using different tools. The first step is determining which text is to be clarified. Many commentators provide their own original translation and textual notes, which explain which ancient versions are being followed. Others use an established English translation as the basis for their comments. The best commentators always refer to the original languages in their research, however. Expositors whose Hebrew is weak, or who do not know Hebrew, should not despair. Most commentaries can be used profitably even without such a knowledge, because most refer to technical details in footnotes, endnotes, or special sections, and, when Hebrew is included in the text, it is usually transliterated into Roman characters and translated into English.
Good commentaries orient readers to the manifold settings of the text. These include historical, archaeological, literary, and theological settings, at least. Knowing about the historical context of the events written about in a text, and what light archaeological excavations might have shed on them, is important for an expositor in establishing a proper framework for interpretation. An expositor should also have confidence in the historical accuracy of the text, and attention to the historical context can help in this regard, as well. The literary and theological settings of the text concern how it fits in with the message of other Biblical books and the major theological motifs of the Bible, and the best commentaries include attention to these, as well.
Good commentaries then take readers through each passage, digging deep into the content of the chapters, paragraphs, and verses. They explain the meanings of the words, phrases, clauses, sentences, and paragraphs, and follow the flow of logic in the text. They take readers back and forth between the "forest" and the "trees" giving proper attention (1) to the broad sweep of the large literary units and the theological messages at this level and (2) to the details of the individual words and phrases. Such commentaries also show how each of two levels interacts with the other.
In many places, texts prove difficult to understand and interpretations vary. The best commentaries discuss these issues, including at least the major alternative interpretations, and then lead readers to a reasoned conclusion.
Commentaries can be broadly divided into three types: exegetical, homiletical, and devotional."Exegesis" can be defined as "the practice of and the set of procedures for discovering the author's intended meaning,"  and I have been describing exegetical commentaries in the remarks above. Homiletical (or "preaching") commentaries are much more self-consciously focused upon making relevant applications of the text to the modern, contemporary world, and they commonly refer to events, ideas, and movements in contemporary culture. As such, they often have an immediate relevance, but they also can become outdated quickly as the culture changes. Most such commentaries are weak concerning the exposition of the text's meaning, compared to exegetical commentaries. Devotional commentaries are often similar, but their focus usually is more individualistic. Often, they are very impressionistic, commenting at random on individual verses or portions of verses, but paying little or no attention to their context.
I recommend that pastors use exegetical commentaries in their sermon preparation. If expositors learn well the message of the text, then many relevant applications should naturally come to mind. Pastors will naturally know their own congregations and immediate cultures much better than most commentators, and so they can easily apply the truths and principles derived from a detailed exegesis of the text to their own context. If homiletical commentaries are used, I recommend they be used where their strengths lie: in bringing in relevant illustrations and making proper application. However, careful expositors - having worked in depth on the text and consulted a few good exegetical commentaries to flesh out their exposition (see below, on "How to Use a Commentary") - will not need to rely on a homiletical commentary's attempts at exegesis, which are almost always weaker than the exegetical commentaries at this point. Furthermore, expositors will be in a good position to evaluate a commentary's success at making proper application, that is, application that faithfully arises from the text at hand. Many points made in application of Biblical truths to modern-day are certainly true, but in too many cases, these points are not supported by the texts appealed to. Expositors firmly rooted in the text itself, supported by a few, judiciously selected chosen commentaries, will be well equipped to make proper and relevant application of the Scriptures to the audiences they minister to.
Caution: Even the best commentaries can be dangerous to expositors' spiritual health and exegetical skills. Why is this? Because, if they become a substitute for the Bible itself, then expositors have abdicated their awesome responsibility of "rightly dividing the word of truth" (2 Tim. ). They have closed their minds to the riches of the Scriptures and have settled for a pale imitation, someone's words about Scripture.
The temptation all too often for expositors is to read the Scripture text through once or twice and then hurry to the commentaries for their insights into the text. The sermon or the lesson becomes a compilation of miscellaneous comments about what different commentators think.
Far better for the expositor to translate the text for himself or herself, to mull over and over again the nuances and flow of thought in the text, reading the original text and the translation 15 - 20 times. For those without knowledge of the original language, far better to read the text in two or three English translations15 - 20 times, and then to devote most of the remaining time - before the actual crafting of the sermon - joy of discovery and the internalizing of the truths of the text in a way that would not be possible by merely perusing various commentaries.
Then, a few commentaries can be consulted in order to shed light on remaining knotty questions, historical context, literary and theological contexts, and possible textual difficulties. Good commentaries contain a wealth of such information. However, expositors do not need a commentary to help them state the obvious, such as "This is what verse 2 says." Expositors should develop their own exegetical skills so that they can use commentaries in those places where they can truly be helpful, and keep from developing an unhealthy dependency on them. Commentaries should be tools of exegesis, not crutches. 
I recommend that pastors practice expository preaching through books of the Bible (or portions of books, if the books are extraordinarily lengthy) as their primary approach to preaching. With this approach, preachers and congregations can be immersed in the overall message of a book in its context, along the lines suggested above, and not just isolated verses or passages.
this is done, then expositors can build up their libraries of commentaries in a
systematic way, as they preach or teach through different books. I recommend that an expositor should own 3 - 5
commentaries on any given book that will be preached or taught in any
depth. Their criteria for evaluation in
purchasing commentaries should keep in mind the discussion above, and include a
commentary's thoroughness, attention to the text'ss message as we have it,
evangelical stance, and all-round usefulness for preaching.
 Walter C. Kaiser, Jr., Toward an Exegetical Theology (Grand Rapids: Zondervan, 1981), 47.
 I hold this point so dearly that, for years, I have required certain seminary classes to write detailed exegetical papers on certain passages without the use of a commentary at all (except for help on the historical context). It is perhaps an extreme measure, but it forces students to read the text on its own terms and to develop their exegetical skills.