When you are preaching the Gospel, you need various tools to help you understand the Biblical text. As noted in other places on this site and others, you should never begin your preparation looking at these tools, however, you should always ensure that your preaching is in line with what is truth. There is nothing that will ruin your credibility faster than basing a major point in your sermon on something that is simply untrue.
When you are attempting to understand the text, you need to know the background of the text, author, occasion that calls for the writing of the scripture. One should never forget that the scripture is an alien book to us. Sometimes we think we are reading a book written primarily to 20th century readers, but there is a gap between us and the original hearers of scripture that require bridging. One important tool in this bridging is the Bible Dictionary. There are a number of dictionaries that can be of aid to the preacher. I personally have Harper-Collins Bible dictionary in addition to Anchor Bible Dictionary on CD. Harper-Collins is one volume and the Anchor is a multi volume tool.
A good Bible dictionary will allow you to look up any word you find in the Bible. That word may be a person, place, or thing. It might be a city. You might wonder about an animal or even the monetary system. Have you thought about the other gods in the surrounding areas of Palestine? All of these questions will be addressed in a good Bible dictionary.
Another Bible dictionary that you can find on the web for free is the International Standard Bible Encyclopedia. However that is a bit dated. in any case, preachers should never preach a text that is not fully understood. While referring to the Bible Dictionary should not be the first place in the sermon prep, you must never get up in the pulpit preaching a text you dont’ understand, a Bible dictionary will help you not make that mistake.