Above all else, guard your heart, for everything you do flows from it. Proverbs 4:23
Whenever there is something wrong with our electrical devices, be it a refrigerator or a computer, we pray that the problem is something minor. What we don't want to hear is that the problem is with the "motherboard." If the motherboard is broken, the rest of the device can't be fixed.
Our hearts are like the motherboard of our beings. The Jewish sages teach that it's not accidental that physically, the heart is centrally located and is responsible for keeping the body alive by pumping blood to the rest of our body. We can have a problem with our foot, our hand, or even something as essential as our eyes. Yet, a person can still live as long as the heart continues to do its job. However, God forbid, if there is a problem with the heart, the entire body and life itself is at stake.
On a spiritual level, the heart is the seat of our emotions, which control our thoughts, which in turn determine our actions. The sages call the heart "the king of the body." It determines our physical health and also what our body parts will do based on our spiritual/emotional health.
Most of us are born with physically healthy hearts, though we might damage it over time. Spiritually, we are likewise born with pure hearts. We naturally love, desire to give, feel appreciation for what we have received, and live happily and trusting. Yet, as time goes on, we can develop spiritual heart conditions that damage our healthy one.
I love this verse in Proverbs: "Above all else, guard your heart, for everything you do flows from it." These are pretty strong words. More than anything else, we have to safeguard our hearts. Like the motherboard of a computer, the heart is the control center; everything we do and everything we are flows from it.
The Bible mentions several spiritual "heart conditions:" a hard heart (Exodus 4:21); a heart of stone (Ezekiel 36:26); a deceitful heart (Jeremiah 17:9); a perverse heart (Proverbs 11:20), and others. Jewish sages also mention a condition known as a "stopped-up heart" where a person's love cannot flow freely.
The key to guarding our hearts is to recognize that they were created pure and good. Our job is to guard our heart; to stop the negative stuff from getting in and to uproot the bad stuff that has made its way in. Don't let in worry, keep out envy, close your heart to temptation, and what you will be left with is a tranquil heart, a trusting heart, and a pure heart that loves God and His people, and behaves accordingly.