Matthew 9: 4 (KJV)
And Jesus knowing their thoughts said, Wherefore think ye evil in your hearts?
Here the Bible says, they thought evil in their heart, and Jesus knew and heard their thoughts, and answered their thoughts. If Jesus could pick evil thoughts, how much more faith thoughts.
Our thoughts are louder before God. God knows what is in your heart. You are a reflection of your thoughts. Look at yourself, see what your thoughts have produced, see the life your thought has produced. You are a products of your thoughts.
1 John 3: 20 (KJV)
For if our heart condemns us, God is greater than our heart, and knoweth all things.
Every thing a man would become or amount to in life are within the boundaries of his thought life. You are as good and productive as your thoughts. Some people did everything, they prayed, fasted, served in church, but they often stumble in their thought life.
Proverbs 4: 23 (NIV)
Above all else, guard your heart, for everything you do flows from it.
John 17: 17 (KJV)
Sanctify them through thy truth: thy word is truth.
Your heart is the production center. The place where everything stem from is your heart. The only material that can sanctify the heart is The Word of God.