For a relatively small organ, weighing only between eight and twelve ounces, the heart holds the responsibility for the health of the whole body—in more ways than one.

Physical
The human heart pumps blood, supplying oxygen and nutrients to the tissue. It also removes carbon dioxide and other waste products that can poison. The tissues of the body need a constant supply of blood in order to be active. If the heart stops pumping, the body dies.

Maybe that’s why we place all kinds of other responsibilities on the heart.

Spiritual
We consider the heart to be the center of the total personality, especially in reference to intuition, feeling, or emotion. We credit it with the capacity for sympathy; feeling; affection. (“Have a heart.” “My heart breaks for you.” “He stole my heart.”)

The word heart is often used to refer to one’s spirit, courage, or enthusiasm. (“She has heart.”)

We talk about memorizing a poem or song lyrics, by heart, meaning it becomes such a part of us that it is easy to recall.

To affirm our integrity or the truth of a statement, we talk about crossing our heart. (“I cross my heart and hope to…”)

We may place so much importance on the heart because God did first.

According to the bible, what is in our heart guides and shapes us.
In 1 Samuel 16:7, the Lord told the prophet, when searching for the next king, not to look at physical stature or attractiveness. “For the Lord sees not as man sees: man looks on the outward appearance, but the Lord looks on the heart.” ESV

God commanded Israel, “Love the Lord your God with all your heart, and with all you soul and with all your might.” God told them he would place this commandment on their hearts. Deuteronomy 6:4-6 ESV

God spoke of the heart being at the center of worship, saying the sacrifices he would honor were “a broken and contrite heart.” Psalm 51:16-17

Jesus warned the heart controls speech and actions. “For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.” Matthew 15:18-20 ESV

He pointed out the dangers of placing too much importance on worldly treasure. “For where your treasure is, there your heart will be also.” Matthew 6:21 ESV

He told of the importance of a good heart. The pure in heart are blessed, because they will see God. (Matthew 5:8)

At belief in Jesus, we not only receive eternal life, we receive the Holy Spirit, who begins the heart purification process.

God assures us his love has been poured into our hearts through the Holy Spirit. (Romans 5:5)