It is true. An example would be. If a man thought there was going to be a lack of something then his thoughts would lead him to be greedy or stingy with what he has. This man's thoughts caused his reaction or actions.
Matthew 15:10-11 - And he called the multitude, and said unto them, Hear, and understand: Not that which goeth into the mouth defileth a man.
Matthew 15:15-20 - Then answered Peter and said unto him, Declare unto us this parable. And Jesus said, Are ye also yet without understanding? Do not ye yet understand, that whatsover entereth in at the mouth goeth into the belly, and is cast out into the draught? But those things which proceed out of the mouth come forth from the heart; and defile the man. For out of the heart proceed evil thoughts, murders, adulteries, fornication, thefts, false witness, blasphemies: These are the things that defile a man; but to eat with unwashen hands defileth not a man.
1 Samuel 16:7 - But the Lord said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the Lord seeth not as man seeth; for man looeth on the outward appearance, but the Lord looketh on the heart.
God has always been especially concerned about man's heart and mind. These few scriptures shows us clearly about the importance of what goes on inside of man. You might kind of wonder, why is it that God cares about what man thinks?
Well the answer is a simple one. Whatever man holds in his heart, or thinks has a tremendous effect upon him in these three areas of his life spiritually, mentally and physically. It's because our heart or mind largely determines what man will ultimately be. The scriptures emphasizes the importance of what man does believes, thinks and feels. This is equally true in our outward as well as our inner man.
A person of godly character doesn't come by favor nor by chance. But it is the natural result of continued effort in right thinking. It's the effect of a long-cherished association with God like thoughts. It is equally true of an ungodly person who has a festival character. By the very same process, is a result of continued harboring of bad or groveling thoughts. I can also add in the apostle Paul's word in Phillippians 4:8-9 - As a man thinketh in his heart, so is he (spiritually, mentally, and physically).
The believers way of life as it directs the mind, and as it controls man's behavior. Will guide or lead man morally and ethically. It constitutes a fine plan of living so far as spiritually, mentally and physically health is concerned. Effect upon the body even as God's laws of cause and effect works in all realms the spiritual, mental and the physical realm. There is no effect without a cause and no cause without it's effect.
Our thoughts control our life so as believers we have to control our thoughts and bring them into obedience to God's Word by taking them captive. Scripture says, "Happy is the man whose mind is stayed on thee".
Colossians 3:1-17; Philippians 4:6-9