God doesn’t exhaust a subject or truth in just one book. God has instead chosen to give us bits and pieces of truth about the same subject in different books throughout the bible. To get an accurate picture of what God is telling you about a particular truth you need to study all the places in the Bible where that particular subject is taught. This is called cross-referencing. A cross-reference is a reference to another Scripture that supports, illuminates, or amplifies the Scripture you are studying. You are comparing Scripture with Scripture, not only for confirmation and revelation, but also to ensure there is no discrepancy in the message.
If there is there’s a contradiction then there’s a problem somewhere because Scripture never contradicts Scripture. A concordance will list all cross-references to a particular Scripture. For serious Bible study you will also need Bible commentaries for both the Old and New Testaments. Before you begin your study of a particular book of the Bible read background information about the book in your commentary. It will give you an introduction to the book along with notes and the message and purpose of the book.
Bible commentaries also tell you who wrote the book along with the approximate date or dates the book was written and where the writing took place. If the book was written to a particular audience the commentaries will document it. You can pick Bible commentaries up in any Christian bookstore or on-line. I find it helpful to read historical books about how the people lived in and around Palestine during the time of Jesus. Understanding local customs and the geo-political system in place at that time gives insight as to why people thought and acted the way they did.