Three reasons why we lie:
We lie to make ourselves look better.
Now a man named Ananias, together with his wife Sapphira, also sold a piece of property.  With his wife's full knowledge he kept back part of the money for himself, but brought the rest and put it at the apostles' feet.
 Then Peter said, "Ananias, how is it that Satan has so filled your heart that you have lied to the Holy Spirit and have kept for yourself some of the money you received for the land?  Didn't it belong to you before it was sold? And after it was sold, wasn't the money at your disposal? What made you think of doing such a thing? You have not lied to men but to God."
 When Ananias heard this, he fell down and died. And great fear seized all who heard what had happened.  Then the young men came forward, wrapped up his body, and carried him out and buried him.
 About three hours later his wife came in, not knowing what had happened.  Peter asked her, "Tell me, is this the price you and Ananias got for the land?"
"Yes," she said, "that is the price."
 Peter said to her, "How could you agree to test the Spirit of the Lord? Look! The feet of the men who buried your husband are at the door, and they will carry you out also."
 At that moment she fell down at his feet and died. Then the young men came in and, finding her dead, carried her out and buried her beside her husband.  Great fear seized the whole church and all who heard about these events. [NIV]
We lie for personal gain.
2 Kings 5:1-27
Now Naaman was commander of the army of the king of Aram. He was a great man in the sight of his master and highly regarded, because through him the Lord had given victory to Aram. He was a valiant soldier, but he had leprosy.
 Now bands from Aram had gone out and had taken captive a young girl from Israel, and she served Naaman's wife.  She said to her mistress, "If only my master would see the prophet who is in Samaria! He would cure him of his leprosy."
 Naaman went to his master and told him what the girl from Israel had said.  "By all means, go," the king of Aram replied. "I will send a letter to the king of Israel." So Naaman left, taking with him ten talents of silver, six thousand shekels of gold and ten sets of clothing.  The letter that he took to the king of Israel read: "With this letter I am sending my servant Naaman to you so that you may cure him of his leprosy."
 As soon as the king of Israel read the letter, he tore his robes and said, "Am I God? Can I kill and bring back to life? Why does this fellow send someone to me to be cured of his leprosy? See how he is trying to pick a quarrel with me!"
 When Elisha the man of God heard that the king of Israel had torn his robes, he sent him this message: "Why have you torn your robes? Have the man come to me and he will know that there is a prophet in Israel."  So Naaman went with his horses and chariots and stopped at the door of Elisha's house.  Elisha sent a messenger to say to him, "Go, wash yourself seven times in the Jordan, and your flesh will be restored and you will be cleansed."
 But Naaman went away angry and said, "I thought that he would surely come out to me and stand and call on the name of the Lord his God, wave his hand over the spot and cure me of my leprosy.  Are not Abana and Pharpar, the rivers of Damascus, better than any of the waters of Israel? Couldn't I wash in them and be cleansed?" So he turned and went off in a rage.
 Naaman's servants went to him and said, "My father, if the prophet had told you to do some great thing, would you not have done it? How much more, then, when he tells you, 'Wash and be cleansed'!"  So he went down and dipped himself in the Jordan seven times, as the man of God had told him, and his flesh was restored and became clean like that of a young boy.
 Then Naaman and all his attendants went back to the man of God. He stood before him and said, "Now I know that there is no God in all the world except in Israel. Please accept now a gift from your servant."
 The prophet answered, "As surely as the Lord lives, whom I serve, I will not accept a thing." And even though Naaman urged him, he refused.
 "If you will not," said Naaman, "please let me, your servant, be given as much earth as a pair of mules can carry, for your servant will never again make burnt offerings and sacrifices to any other god but the Lord.  But may the Lord forgive your servant for this one thing: When my master enters the temple of Rimmon to bow down and he is leaning on my arm and I bow there also--when I bow down in the temple of Rimmon, may the Lord forgive your servant for this."
 "Go in peace," Elisha said.
After Naaman had traveled some distance,  Gehazi, the servant of Elisha the man of God, said to himself, "My master was too easy on Naaman, this Aramean, by not accepting from him what he brought. As surely as the Lord lives, I will run after him and get something from him."
 So Gehazi hurried after Naaman. When Naaman saw him running toward him, he got down from the chariot to meet him. "Is everything all right?" he asked.
 "Everything is all right," Gehazi answered. "My master sent me to say, 'Two young men from the company of the prophets have just come to me from the hill country of Ephraim. Please give them a talent of silver and two sets of clothing.' "
 "By all means, take two talents," said Naaman. He urged Gehazi to accept them, and then tied up the two talents of silver in two bags, with two sets of clothing. He gave them to two of his servants, and they carried them ahead of Gehazi.  When Gehazi came to the hill, he took the things from the servants and put them away in the house. He sent the men away and they left.  Then he went in and stood before his master Elisha.
"Where have you been, Gehazi?" Elisha asked.
"Your servant didn't go anywhere," Gehazi answered.
 But Elisha said to him, "Was not my spirit with you when the man got down from his chariot to meet you? Is this the time to take money, or to accept clothes, olive groves, vineyards, flocks, herds, or menservants and maidservants?  Naaman's leprosy will cling to you and to your descendants forever." Then Gehazi went from Elisha's presence and he was leprous, as white as snow. [NIV]
We lie to avoid negative consequences.
When Moses approached the camp and saw the calf and the dancing, his anger burned and he threw the tablets out of his hands, breaking them to pieces at the foot of the mountain.  And he took the calf they had made and burned it in the fire; then he ground it to powder, scattered it on the water and made the Israelites drink it.
 He said to Aaron, "What did these people do to you, that you led them into such great sin?"
 "Do not be angry, my lord," Aaron answered. "You know how prone these people are to evil.  They said to me, 'Make us gods who will go before us. As for this fellow Moses who brought us up out of Egypt, we don't know what has happened to him.'  So I told them, 'Whoever has any gold jewelry, take it off.' Then they gave me the gold, and I threw it into the fire, and out came this calf!" [NIV]
At the end of the forty days and forty nights, the Lord gave me the two stone tablets, the tablets of the covenant.  Then the Lord told me, "Go down from here at once, because your people whom you brought out of Egypt have become corrupt. They have turned away quickly from what I commanded them and have made a cast idol for themselves."
 And the Lord said to me, "I have seen this people, and they are a stiff-necked people indeed!  Let me alone, so that I may destroy them and blot out their name from under heaven. And I will make you into a nation stronger and more numerous than they."
 So I turned and went down from the mountain while it was ablaze with fire. And the two tablets of the covenant were in my hands.  When I looked, I saw that you had sinned against the Lord your God; you had made for yourselves an idol cast in the shape of a calf. You had turned aside quickly from the way that the Lord had commanded you.  So I took the two tablets and threw them out of my hands, breaking them to pieces before your eyes.
 Then once again I fell prostrate before the Lord for forty days and forty nights; I ate no bread and drank no water, because of all the sin you had committed, doing what was evil in the Lord's sight and so provoking him to anger.  I feared the anger and wrath of the Lord, for he was angry enough with you to destroy you. But again the Lord listened to me.  And the Lord was angry enough with Aaron to destroy him, but at that time I prayed for Aaron too.  Also I took that sinful thing of yours, the calf you had made, and burned it in the fire. Then I crushed it and ground it to powder as fine as dust and threw the dust into a stream that flowed down the mountain. [NIV]
Now Peter was sitting out in the courtyard, and a servant girl came to him. "You also were with Jesus of Galilee," she said.
 But he denied it before them all. "I don't know what you're talking about," he said.
 Then he went out to the gateway, where another girl saw him and said to the people there, "This fellow was with Jesus of Nazareth."
 He denied it again, with an oath: "I don't know the man!"
 After a little while, those standing there went up to Peter and said, "Surely you are one of them, for your accent gives you away."
 Then he began to call down curses on himself and he swore to them, "I don't know the man!"
Immediately a rooster crowed.  Then Peter remembered the word Jesus had spoken: "Before the rooster crows, you will disown me three times." And he went outside and wept bitterly. [NIV]
Three reasons why we shouldn’t lie:
God hates it.
There are six things the Lord hates,
seven that are detestable to him:
 haughty eyes,
a lying tongue,
hands that shed innocent blood,
 a heart that devises wicked schemes,
feet that are quick to rush into evil,
 a false witness who pours out lies
and a man who stirs up dissension among brothers. [NIV]
The Lord abhors dishonest scales,
but accurate weights are his delight. [NIV]
A truthful witness gives honest testimony,
but a false witness tells lies.
 Reckless words pierce like a sword,
but the tongue of the wise brings healing.
 Truthful lips endure forever,
but a lying tongue lasts only a moment.
 There is deceit in the hearts of those who plot evil,
but joy for those who promote peace.
 No harm befalls the righteous,
but the wicked have their fill of trouble.
 The Lord detests lying lips,
but he delights in men who are truthful. [NIV]
It’s an indicator of who we are following.
To the Jews who had believed him, Jesus said, "If you hold to my teaching, you are really my disciples.  Then you will know the truth, and the truth will set you free."
 They answered him, "We are Abraham's descendants and have never been slaves of anyone. How can you say that we shall be set free?"
 Jesus replied, "I tell you the truth, everyone who sins is a slave to sin.  Now a slave has no permanent place in the family, but a son belongs to it forever.  So if the Son sets you free, you will be free indeed.  I know you are Abraham's descendants. Yet you are ready to kill me, because you have no room for my word.  I am telling you what I have seen in the Father's presence, and you do what you have heard from your father."
 "Abraham is our father," they answered.
"If you were Abraham's children," said Jesus, "then you would do the things Abraham did.  As it is, you are determined to kill me, a man who has told you the truth that I heard from God. Abraham did not do such things.  You are doing the things your own father does."
"We are not illegitimate children," they protested. "The only Father we have is God himself."
 Jesus said to them, "If God were your Father, you would love me, for I came from God and now am here. I have not come on my own; but he sent me.  Why is my language not clear to you? Because you are unable to hear what I say.  You belong to your father, the devil, and you want to carry out your father's desire. He was a murderer from the beginning, not holding to the truth, for there is no truth in him. When he lies, he speaks his native language, for he is a liar and the father of lies.  Yet because I tell the truth, you do not believe me!  Can any of you prove me guilty of sin? If I am telling the truth, why don't you believe me?  He who belongs to God hears what God says. The reason you do not hear is that you do not belong to God." [NIV]
"As the Father has loved me, so have I loved you. Now remain in my love.  If you obey my commands, you will remain in my love, just as I have obeyed my Father's commands and remain in his love.  I have told you this so that my joy may be in you and that your joy may be complete.  My command is this: Love each other as I have loved you.  Greater love has no one than this, that he lay down his life for his friends.  You are my friends if you do what I command.  I no longer call you servants, because a servant does not know his master's business. Instead, I have called you friends, for everything that I learned from my Father I have made known to you. [NIV]
Therefore each of you must put off falsehood and speak truthfully to his neighbor, for we are all members of one body. [NIV]
Do not lie to each other, since you have taken off your old self with its practices  and have put on the new self, which is being renewed in knowledge in the image of its Creator.  Here there is no Greek or Jew, circumcised or uncircumcised, barbarian, Scythian, slave or free, but Christ is all, and is in all. [NIV]
We become slaves to it, and it robs us of our freedom.
A false witness will not go unpunished,
and he who pours out lies will not go free. [NIV]
When we put bits into the mouths of horses to make them obey us, we can turn the whole animal.  Or take ships as an example. Although they are so large and are driven by strong winds, they are steered by a very small rudder wherever the pilot wants to go.  Likewise the tongue is a small part of the body, but it makes great boasts. Consider what a great forest is set on fire by a small spark.  The tongue also is a fire, a world of evil among the parts of the body. It corrupts the whole person, sets the whole course of his life on fire, and is itself set on fire by hell.
 All kinds of animals, birds, reptiles and creatures of the sea are being tamed and have been tamed by man,  but no man can tame the tongue. It is a restless evil, full of deadly poison.
 With the tongue we praise our Lord and Father, and with it we curse men, who have been made in God's likeness.  Out of the same mouth come praise and cursing. My brothers, this should not be.  Can both fresh water and salt water flow from the same spring?  My brothers, can a fig tree bear olives, or a grapevine bear figs? Neither can a salt spring produce fresh water. [NIV]
Then you will know the truth, and the truth will set you free." [NIV]
Taking it to work:
What a man desires is unfailing love;
better to be poor than a liar.
 The fear of the Lord leads to life:
Then one rests content, untouched by trouble. [NIV]
A fortune made by a lying tongue
is a fleeting vapor and a deadly snare. [NIV]
Then he called the crowd to him along with his disciples and said: "If anyone would come after me, he must deny himself and take up his cross and follow me.  For whoever wants to save his life will lose it, but whoever loses his life for me and for the gospel will save it.  What good is it for a man to gain the whole world, yet forfeit his soul?  Or what can a man give in exchange for his soul? [NIV]