The Bible sites the importance of the condition of our hearts many, many times. One good example is John 14:27 "Peace I leave with you; my peace I give you.1 I do not give to you as the world gives. Do not let your hearts be troubled2 and do not be afraid."
Fear is a block to all good things. When you can fantasize (pray) with your mind in a way that touches your heart, miracles happen. When God said Matthew 21:22 NIV "If you believe, you will receive whatever you ask for in prayer." He meant in a way that connects with your heart.
Believing with your mind is one thing. Believing with you heart; that kind of believing we had as children the night before Christmas, is quite another. Remember the excitement you felt, the butterflies in your stomach? That's what brings about change.
It is true where the heart leads the man follows. So guard you heart against vain imaginings and set it on fantasizing freedom from fear and evil forboding. Freedom to love and live as fully as possible.