Matthew 12:34 says:

Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks.

Your heart is your spirit.  You are a spirit.  You have a soul, and you live in a physical body.  You are a tripartite creature.  In other words, you are composed of three parts.  With those three parts, you actually contact three worlds.  With your spirit, you contact the world, or realm of God.  Jesus says in John 4:24, "God is Spirit, and those who worship Him must worship in spirit and truth."  Genesis 1:26 tells us, "Then God said, "Let Us make man in Our image, according to Our likeness...."  If God made us in His image, then we must be like God.  God is a Spirit.  Therefore, we also are spirits.

Genesis 1:26 could not be talking about our being made physically in God's image.  If we looked like God physically, then God would be a monstrosity.  He would have a white face, a black body, red arms, brown legs, and yellow feet, because those are the five major classifications of mankind on the earth.  That would be ridiculous.  God is a Spirit, so when Genesis says that we were made in God's image; it means we were created as spirits.

When the Bible speaks of the heart, it is not talking about the muscle that pumps blood through your body.  The Bible often uses the word heart figuratively, referring to the center or core of your being.  When we talk about the heart of a melon, the heart of a tree, or the heart of a problem, we are talking about the center and core of those things.  When the Bible talks about the heart of man, it is talking about the center and core of man.  What is man at his center or core?  He is a spirit.  When the Bible talks about your heart, therefore, it is really talking about your spirit.

With this information in mind, read Matthew 12:34 once more, and let me point out something of the utmost importance to us as Christians.

Brood of vipers! How can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks.

In other words, out of the abundance of your spirit, your mouth will speak.  If your mouth is not speaking right, something must be wrong with what is inside of you.

Someone may say, "Well, Brother Price, the Lord knows I have a praise in my heart, and that I don't do much taking."  The Lord also knows that person just lied.  The Bible says, "For out of the abundance of the heart the mouth speaks."  If the mouth is not speaking, it must be because there is nothing in the heart. 

We can, therefore, measure a man's spirit by his mouth.  Of course, we should live right, and act right, but sometimes people can fool you with their actions.  They can seem to be one thing, and can actually be something else.  Sooner or later, however, their mouths will give them away, because their mouths will speak what is in their hearts.  If you have an evil heart, you cannot speak good things.

Jesus amplifies this concept still further in Matthew 12:35-37:

35 "A good man out of the good treasure of his heart brings forth good things, and an evil man out of the evil treasure brings forth evil things

36 "But I say to you that for every idle word men may speak, they will give account of it in the day of judgment

37 "For by your words you will be justified, and by your words you will be condemned."

The word idle, in verse 36, means useless, negative, non-productive.  In other words, idle words are words that have no value; they do not edify you or build you up.  They do not do any good for you.  And, according to Jesus, we have to give an account of those words in the day of judgment: "For by your words you will be justified, and by your words you will be condemned."

Isn't it interesting that Jesus does not say we are justified or condemned by our deeds, but by our words?  That is an awesome statement.  The reason Jesus says, "by your words," is that your deeds will be based on your words.  Ultimately, if you continue talking badly, you are going to act badly.  If you keep talking sickness, you will have sickness.  Keep talking failure, and you will fail.

We can see very clearly here how important our words really are.  We not only affect our lives by what we say, but we are also judged by it.  By our words, we can either be justified or condemned.