If you allow your heart to be filled with thoughts of doubt, fear, and unbelief regarding the circumstances you are facing, it will be manifested through the words you speak and you will not be able to receive what you need from God because of the unbelief in your heart.

The heart is the center of man's existence. It is in the heart man receives the Word, is convicted by the Holy Spirit, and is saved (Romans 10:8-10). It is in the heart — within man's innermost being — where he either has faith to believe God's Word and His promises, or harbors doubt and unbelief that hinders him from receiving what he needs from God. Jesus said:

Have faith in God. “Truly I say to you, whoever says to this mountain, “Be taken up and cast into the sea,” and does not doubt in his heart, but believes that what he says is going to happen, it shall be granted him. (Mark 11:22-23, NAS)

What is in your heart and mind determines what you are. Jesus taught the multitudes that it is possible to sin in the heart, the innermost being, even before the sin is manifested outwardly. He said:

But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. (Matthew 5:28)

It is in man's heart — his innermost being — where sin is conceived. It was in Satan's heart that sin originated. His heart was lifted up because of his beauty (Ezekiel 28:17). It was in his heart that he exalted himself above God. (Isaiah 14:13-14).

When Ananias and Sapphira lied about the sale of their land and kept back part of the money for themselves, Peter asked, “But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land?” (Acts 5:3).

The Greek word for heart is kardia which includes man's entire mental and moral activity, the inner man. It is recognized as the place where the emotions, desires, perceptions, thoughts, understanding, reasoning powers, conscience, intentions, the will, and imagination reside.

Peter asked Ananias, “How is it that Satan has so filled your heart?” In other words, he was asking, “Why have you allowed Satan to so fill your innermost being, your heart, mind, your thoughts that you lied to the Holy Spirit? The thoughts Ananias and Sapphira allowed Satan to plant in their hearts took root, sin was conceived in their hearts, and sin was manifested through their actions.

What is in a man's heart and mind determines what he is, “For as he thinketh in his heart, so is he…” (Proverbs 23:7). In this verse we see that the word “heart” is used to refer to the place where man's thoughts originate. How's your thinking today?

What is in my heart determines who I am. I will think today on only things that edify. I will bring every thought under the control of the Holy Spirit.