Occasionally I'm asked by both seminary students and people at church about the use of commentaries in one's personal study of the Bible. First, let's define what a commentary is: Commentaries are books that contain comments (observations) on the biblical text. Usually the comments are arranged in verse order, that is, in the same order as the text of the Bible.
Commentaries come in lots of different varieties. There are different levels of difficulty, different target audiences, different emphases, and different lengths. Some commentaries are part of a set (for example, the New American Commentary or the Word Biblical Commentary) whle other commetaries a individual volumes on a single book of the Bible (sometimes called a "stand-alone" commentary as opposed to a volume in a series). Other biblical commentaries are called "one-volume" commentaries because the entire Bible is covered in one (or maybe two) volumes, ususally pretty thick. Examples of one-volume commentaries are the Wycliffe Bible Commentary or the New Bible Commentary.
Commentaries can be divided by level of difficulty: At the top of the pyramid are the "full technical" or "critical" commentaries which often have very detailed and technical discussions and assume the reader knows the original biblical languages (Hebrew, Aramaic, Greek) to some extent. These are used mostly by scholars, seminary students, and pastors with some language training. These are usually difficult for the non-specialist to read and understand. Many of them provide their own translation into English from the biblical languages. Examples of these are the International Critical Commentary, the Word Biblical Commentary, the Hermeneia Commentary, the New International Greek Testament Commentary, and the Anchor Bible Commentary.
Next there are commentaries that are sometimes called "semi-technical" because while they refer to some technical details, reference to Hebrew and Greek is occasional and usually confined to the footnotes rather than the text itself. A well-educated lay person can often read and follow these discussions, though some things would still be somewhat hard to understand. Usually these commentaries are based on a particular English translation for the entire series, like the NIV or RSV. Examples of "semi-technical" commentaries would be the New International Commentary on the New Testament and the New American Commentary.
Although we could consider them closely related to the "semi-technical" commentaries, there are so-called "pulpit" commentaries which are intended to give special help to pastors and teachers in developing sermons, so there is an emphasis on insights useful for preaching. Among these are the Preacher's Commentary Series and the Pillar New Testament Commentary. The New American Commentary could also be placed here. These too are usually based on an existing English translation.
Then there are commentaries intended primarily for general readers. These have a less technical focus, are more applicational in nature, and sometimes devotional. There is quite a range here, from the IVP New Testament Commentary, the Expositor's Bible Commentary, and the Tyndale New Testament Commentaries to the Life Application Bible Commentary. Among commentaries intended for general readers are the short one and two volume commentaries like the Wycliffe Bible Commentary, the New Bible Commentary, and the Bible Knowledge Commentary. These may not have much detail on a given passage, but will usually highlight the major points and key issues with a few different interpretive options in some cases. They can be especially helpful if you don't have much time to study a given passage but need a general knowledge of what it is talking about.
Although some Bible students shy away from using commentaries, not wanting to be "influenced" by the teaching of others, commentaries provide a good way to check your own understanding of scripture and your own interpretations of passages. They help even the casual user to avoid misunderstandings and mistakes about the Bible. They can also help you get a better grasp of major Bible themes and topics and see the flow of the author's argument better in a given passage of scripture. If you are concerned about being unduly influenced by a particular commentary, I recommend you read two or three on the same passage, which will serve as a "check and balance" on one another.
Of course, the notes that accompany the NET Bible First Edition (full edition) both in print and online contain references to many commentaries, both individual ones and series, and in some cases provide pretty thorough commentary in the notes themselves. The NET Bible translators and editors have summarized and "pre-digested" much commentary material and selected for inclusion in the notes only what is most essential. But if you want to go deeper than the NET Bible notes allow, then you should consult some of the various kinds of commentaries we've discussed.
One of my favorite quotations about commentaries which I share every year with my students comes from the great preacher of Victorian England, Charles Spurgeon, who gave many lectures for preachers and Bible students, so I'll close for now with that. This is what Spurgeon said "On Commenting and Commentaries":
"In order to be able to expound the Scriptures, and as an aid to your pulpit studies, you will need to be familiar with the commentators: a glorious army, let me tell you, whose acquaintance will be your delight and profit. Of course, you are not such wiseacres as to think or say that you can expound Scripture without assistance from the works of divines and learned men who have laboured before you in the field of exposition. If you are of that opinion, pray remain so, for you are not worth the trouble of conversion, and like a little coterie who think with you, would resent the attempt as an insult to your infallibility. It seems odd, that certain men who talk so much of what the Holy Spirit reveals to themselves, should think so little of what he has revealed to others."