Bible commentaries are an essential tool for personal Bible study and Bible exposition. There are those who would vehemently disagree with that previous sentence. But do not listen to them. Commentaries are important and helpful.
I strive to live by the principle of the Proverbs that teach the importance of godly counsel (e.g., Proverbs 11:141; 15:22; 20:18). This is one of the reasons why I use Bible commentaries. There are men who have spent decades studying particular books of the Bible. And it is foolish and arrogant for us to think that we would not be aided by consulting those who have spent so long with particular sections of scripture and have published their studies.
Of course, you must not be a slave to commentaries. In fact, it is wise to use them last, after you have gone through your own process of studying the meaning of the text. This will keep you from merely parroting or echoing other people's ideas. You and your Sunday school class and your congregation and whoever else you are responsible for teaching need to know what God has taught you about the text and its application - not merely what he has taught John MacArthur, Warren Wiersbe, James Montgomery Boice, and others.
Likewise, you should be careful in your selection of commentaries. Most of us do not have the money to buy unhelpful books (if there is such a thing). And some books are really not worth spending a lot of time with. Sunday is coming fast. And you don't have a lot of time to waste. So your goal is to have access to the best resources for the passage that you are studying.
To that end, I have found a website that reviews and recommends best commentaries. It's called Best Commentaries. Check it out. And bookmark it for later reference.
I learned of this site by Tim Challies recommendation on his website.
If you know of other helpful online studies tools and resource sites, pass them on.