People sometimes say, ‘A man is only as good as his word.’ What do they mean when they say that? ‘You can judge whether a man is good or bad by how well he keeps his promises.’ We can not trust* a person who does not tell the truth. A person who lies can do great harm. 
Remember that the first four commands teach us how to love God. The last six commands tell us how to love our neighbors. If we love our neighbor, we will not tell lies about them.
We break the ninth command when we lie. But there are other ways to break the command as well. One way is to boast. We say things about ourselves that are not entirely true. We say something to make us seem smarter or stronger or wiser than we are.
Sometimes, a person will lie to get more money. They will say things that are not true about what they want to sell. They may gain money that way, but they can not earn a good conscience that way. 
Slander is another way we break the ninth command. We tell stories about someone that are not true. Or we tell only part of the truth about someone. We want people to think badly about that person. God is not pleased with this. He tells us that a person who speaks in this way is a fool.
There are many reasons people lie. Sometimes we lie because the truth would bring us shame. We make a mistake. We do something bad, so we do not want people to know what we have done. We care too much about what other people will think of us. We are proud. So, we lie so we will not feel shame.
The Bible* tells us that God always keeps his promises. We can always trust that what he says is true. The scriptures* tell us that God can not lie. We can always believe what he says.  The God who made us is the ‘God of truth.’ He is always tells the truth in his speech and his actions. So, if we are to be his people, we must be honest.
Lying starts in the heart.* We begin lying early in our lives. David* says that we are born speaking lies. Because God knew that this was a problem, he gave his people this command. He wanted them to be people who tell the truth.
The Evil One* was the first person to tell a lie. He told Eve* that God did not mean what he said. God had told Adam* not to eat from the tree in the middle of the garden. ‘If you eat from that tree,’ God said, ‘You will certainly die.’ But the Evil One told her a lie. He said that she would not die. Instead, if she ate from the tree, she would be like God. Because the Evil One lied and Eve listened, God was not pleased. Adam and Eve had to leave the place God made for them. And every bad thing that we know about today came into the world. Now, the Bible says that all people tell lies, just like the Evil One.
Many years after God gave Moses* this law*, the prophets* reminded the people of the command. ‘Speak the truth to one another. Make right and wise decisions in your courts. Do not make evil plans against one another. When you promise to tell the truth, do not lie. Many people love to do that. But I hate all these things, says the Lord.’ * If we continue to lie and do not speak the truth, God will not welcome us to be with him 
People who follow God are people who tell the truth.
 Proverbs 25:18
 Mark 12:30-31
 Proverbs 21:6
 Proverbs 10:18
 Titus 2:1; Hebrews 6:19
 Isaiah 65:16
 Matthew 15:18-19
 Psalm 58:3
 Genesis 3:1-6
 John 8:44; Psalm 116:11
 Zechariah 8:16-18