HERE is a post in which Tim Bulkeley discusses the use of Bible dictionaries and Bible commentaries.  He gives some very good advice, which has served me well when interpreting  given passages. “So on the whole avoid consulting commentaries as long as you can. The more you work at a text before reading one the more chance you have of arriving at a destination determined by the text that is different from the one the commentator recommends ;).”  This is similar to (though not quite the same as) the advice I received from the professor for whom I was once a teaching assistant.  He said that if you have done your work properly, a commentary should confirm many of your findings (assuming that the commentator has done their work well).  My bottom-line: Don’t use a commentary to be lazy and not study a passage for yourself.