that the man of God may be complete, thoroughly equipped for every good work.
2 Timothy 3:16-17 (NKJV)
When I was in school, we took tests for the different classes that we had. Sometimes, we had what they called an open book test. This was a test that was different from the usual tests, because we were allowed to use our textbooks to look for the answers to the questions. This was a much easier test, unless you did not know what was in the textbook. If you had read the textbook for the class, and you knew what was taught about the subject at hand, the open book test was easy to successfully complete.
In 2 Timothy 3:16, Paul wrote to Timothy about four different things that God's Word is profitable for: doctrine, reproof, correction, and instruction in righteousness. These four things fit into two different categories: beliefs, and actions. Doctrine and correction here are talking about having right and wrong beliefs, and instruction in righteousness and reproof are talking about right and wrong behavior. God's Word shows us the right things to believe and do, as well as showing us the wrong kinds of beliefs and actions to avoid.
God's Word shows us right and wrong beliefs, and actions, so it really is simple for us to understand what we should and should not do, as well as seeing what is right to believe and what is not. The Christian life is like an open book test, where we go through life and whatever challenge we face we can go to God's Word to see what we need to do. Life can be challenging and testing at times, but we have an open book, the Bible, that helps to show us the answers we need to the questions we face in life.