1) Out of it are the issues of life.
Proverbs 4:23 says, Keep thy heart with all diligence; for out of it are the issues of life. So, what exactly does that mean? It means that our thoughts, actions, attitudes, and feelings are all dependent on the condition of our heart. A bitter heart leads to a bitter attitude, negative thoughts and feelings, and wrong actions. The same can be said of a hard heart or a resentful heart. Everything we are and everything we do is a reflection of what's in our heart. If we want a happy and peaceful life that is obedient to God, then we need to guard our heart against any influence that would destroy that happiness, peace or obedience.
2) It is the source of our words.
We often think of our brains as the source of our thoughts and words, but according to the Bible, that's not really the case. And if you think about it, I'm sure you'll agree that we've all said some things that seemed to bypass the brain before coming out of our mouths, right? Luke 6:45 reminds us A good man out of the good treasure of his heart bringeth forth that which is good; and an evil man out of the evil treasure of his heart bringeth forth that which is evil: for of the abundance of the heart his mouth speaketh. The things that find their way into our hearts will eventually find their way out of our mouths. And we all know that once those hateful, bitter words have been spoken, we cannot take them back. The damage is done. Guarding our hearts is an essential part of making sure that we don't say things that we shouldn't say because the mouth will utter whatever the heart contains. A good heart equals good words. A bad heart? Well, you know the answer.
3) It is deceitful and desperately wicked.
It is imperative that we guard our hearts because they are naturally drawn to evil things. They cannot be trusted to do the right thing. We learn this in Jeremiah 17:9 which says, The heart is deceitful above all things, and desperately wicked: who can know it? The heart wants what the heart wants whether it's a good thing or night. That is one reason I grow so aggravated when I hear someone giving the advice, "Well, you ought to just follow your heart." No, you shouldn't! Why would you follow something that God says is deceitful and desperately wicked? He goes on to say in Proverbs 28:26, He that trusteth in his own heart is a fool. . . Our hearts will lie to us. They will promise us great things, but in the end, all we will receive is disappointment and guilt. We must guard our hearts against outside evil influences and even from itself. Our hearts cannot be our guide through life. That's God's place.
Knowing this, is it any wonder God cautions us to daily take up our armor, including the breastplate of righteousness. The world is out to get us. Satan is out to destroy us. Even our own flesh is against us. Every day is a spiritual battle, and we must be armed and ready to defend ourselves and our faith. Guard your heart today, my friend!