God has given us His Word as a guide for our life. However, His Word won't help us if we don't study it, know it, and live by it. Therefore, we must diligently study and apply God's Word if we wish for it to have an impact on our lives.
Jesus promised, "If you abide in My word ..., you are truly My disciples. And you will know the Truth, and the Truth will set you free" (John 8:31-32, AMP). That's a promise that if we abide in His Word, we will know the Truth, because His Word is the Truth.
So it makes sense that God told the Israelites, "Do not let this Book of the Law depart from your mouth; meditate on it day and night, so that you may be careful to do everything written in it. Then you will be prosperous and successful" (Joshua 1:8).
Joshua later repeated a similar instruction: "Be careful to obey all that is written in the Book of the Law of Moses, without turning aside to the right or to the left" (Joshua 23:6).
Why is it so important to follow God's Word? Because His Word keeps us from turning aside to the right or to the left; it keeps us on the straight and narrow path that leads to life (see Matthew 7:13-14).
Therefore, abide in His Word, because His Word will keep you from sin.