Guy Davies has a helpful discussion on sermon preparation in general and the use of commentaries in particular. In the post, Guy notes nine "dangers of commentaries." I have reproduced an edited form of his comments below.
Commentators sometimes go to great lengths on "easy bits" of the Bible, while passing over more difficult passages where most help is needed.
2) Vain discussion
Some commentaries pay too much attention to scholarly fads. Biblical scholars should write with pastors in mind and pay attention to 1 Timothy 1:4 & 1 Timothy 6:20.
3) Weak exegesis
Even the best commentators may be wrong.
4) Weak in biblical integration Little feel for redemptive-historical issues.
No suggestions as to how OT texts speak to NT believers. Preachers are especially in need this kind of help.
5) Failure to point to Christ A sad failing in some modern evangelical OT commentaries. Symptomatic of the influence of unbelieving scholarship. The Old Testament is about Christ (John 5:46). Evangelical commentators above all should attempt to show how the OT is fulfilled in Jesus (Luke 24:44).
6) Often weak in application
As John Frame says, "meaning = application." A commentary that fails to apply the text has not made the meaning clear. Another area where pastors look for help.
7) Concessions to unbelieving theology
Historicity of OT events questioned. Pauline authorship denied.
Scholarly commentaries can sometimes be a little dull. Preachers must not be. Avoid the danger of "the bland leading the bland."
9) Turn the handle mentality
Commentaries are no substitute for a prayerful and reflective engagement with Holy Scripture.
Read the entire post here.