Satan is the father of lies: "You are of your father the devil, and you want to do the desires of your father. He was a murderer from the beginning and does not stand in the truth, because there is no truth in him. Whenever he speaks a lie, he speaks from his own nature; for he is a liar, and the father of lies" (John 8:44). Just as God's nature is truth (Titus 1:2), so Satan's nature is falsehood. It was by false witness that Satan tempted man into ruin.
Now the serpent was more cunning than any beast of the field which the Lord God had made. And he said to the woman, "Has God indeed said, 'You shall not eat of every tree of the garden'?" 2 And the woman said to the serpent, "We may eat the fruit of the trees of the garden; 3 but of the fruit of the tree which is in the midst of the garden, God has said, 'You shall not eat it, nor shall you touch it, lest you die.' " 4 Then the serpent said to the woman, "You will not surely die. 5 For God knows that in the day you eat of it your eyes will be opened, and you will be like God, knowing good and evil." 6 So when the woman saw that the tree was good for food, that it was pleasant to the eyes, and a tree desirable to make one wise, she took of its fruit and ate. She also gave to her husband with her, and he ate. ―Genesis 3:1-6
At the root of every sin is a lie. "For out of the heart come forth evil thoughts...false witness, railings: these are the things which defile the man" (Matt. 15:19-20).
The truth is simple; the lie is complicated. We don't trip when telling the truth but managing a lie can get out of control. The truth is easy to remember; the lie involves too many fabricated details. Thus, the false witness frequently stumbles and is revealed. "He who utters truth shows forth righteousness, but a false witness deceit.... The lip of truth shall be established forever, but a lying tongue is but for a moment" (Proverbs 12:17, 19).
God's word is always consistent with God's actions. We expect to see God act in a consistent way with His words. Since God's words and actions are consistent with one another, we say that God is trustworthy. Likewise, a man's words are indicative of his trustworthiness. You are as good as your word. A man who would lie would probably steal. In other words, a false witness cannot be trusted in any area of life. The so-called "little white lies" that we are prone to tell are also a reflection of our character. If you cannot be trusted in the little things, then why should you be trusted in the big things? The righteous man is described in Psalm 15 as one who "swears to his own hurt, and does not change."
Deception is lying to others and self-deception is lying to yourself; convincing yourself of a falsehood. Selfishness motivates sinners to believe what they want to believe about themselves. This is often done to justify some desire, attitude or action, and so, we spin the truth (which is a lie), in order to excuse ourselves. We engage in a cover-up. Truth loves the light, the lie loves the darkness.
Truthful words are essential to healthy relationships. "You shall not bear false witness against your neighbor" (Ex. 20:16; Dt. 5:20; Matt. 19:18). The tongue is our interface with the world. "For the mouth speaks out of that which fills the heart" (Matt. 12:34). We are called to "speak the truth in love" to one another (Eph. 4:15). "You shall not...lie one to another" (Leviticus 19:11). The power and character of your words either builds or destroys, "A man who bears false witness against his neighbor is a maul, and a sword, and a sharp arrow" (Proverbs 25:18). "You shall not take up a false report; put not your hand with the wicked to be an unrighteous witness" (Exodus 23:1). "Wherefore, putting away falsehood, speak the truth each one with his neighbor, for we are members one of another" (Ephesians 4:25). "Lie not one to another, seeing that you have put off the old man with his doings" (Colossians 3:9).
"There are six things which Jehovah hates, yes seven which are an abomination to Him: haughty eyes, a lying tongue...a false witness who utters lies" (Proverbs 6:16-19). Be scrupulous in what you say. Your word is one of the precious possessions you have. Treasure it.