You should, even if you don't know what it is.
A concordance is a resource book that offers an alphabetical listing of words present in a text. For instance, you want to find all the passages that mention the word "bread" in the Bible. You open your concordance to "bread", and there they are.
Now, concordances can be a little pricey, as they are reference books (hunt around on Amazon). But if you're like me, you'll use it so often that you'll justify the price. Even if you simply use it for your own spiritual enrichment, you'll be happy you bought one.
I happen to own this one, and would happily recommend it.