Truth is an essential part of God's character.  Jesus Christ described Himself as 'the Truth' (John 14:6).  But falsehood is an essential part of the devil's character; and lying is his native language (John 8:44-45).  Therefore, everybody who belongs to Jesus has an obligation to stop lying and speak the truth.  Continuing to lie, after we are saved, is a terrible insult to our Creator: it shows that we care more about how we can elevate ourselves and manipulate our own circumstances than desire His glory and trust in His sovereign power.
 
Lying is addictive and easily becomes a habit, or even a way of living!  It puts its roots deep into our desires and thoughts, to corrupt our communication at every level.  But when we submit to Jesus, He puts truth into our hearts, disturbing the roots of falsehood.  As we get to know Him better, we realise that lies cannot remain in His presence and that our spiritual lives will shrivel unless we embrace and express truth. Any lie plays into the devil's hand.

When we submit our lives to Jesus, it is as though we take off our old set of dirty clothes which are stained with sinful desires and behaviour.  Then we put on a new set of clothes, given to us by the Lord, which will honour Him.  The parable of the prodigal son makes this clear as the Father embraces the filthy swineherd in love but then says, '“Quick! Bring the best robe and put it on him. Put a ring on his finger and sandals on his feet. Bring the fattened calf and kill it. Let’s have a feast and celebrate. For this son of mine was dead and is alive again; he was lost and is found.” So they began to celebrate.' (Luke 15:22-24)   What a tragedy it would have been for the forgiven son to even want to wear his old dirty and smelly clothes again.  
 
Lying is part of the old set of clothes.  It must stop!  Although the Holy Spirit makes us unsettled about lying, our sinful nature will want to retain the right to control our destiny by using lies.  Radical surgery is needed to remove it, and repeated until the habit is broken.  First, we must agree with God's Word that lies are bad.  We must repent of thinking that little lies, white lies, exaggerations and 'helpful' lies are all right: in fact, they contribute to Satan's destructive work.  Then we need to ask the Lord to change our heart to hate lies and love the truth (Psalm 51:10).  Then keep checking what comes out of our mouths, asking the question, ‘Was that completely true?’  If it was not, then repent.  If it was, then give thanks that God is working His truth into you.  Pray that you will value truth, even in a culture where lying seems to be endemic.  Be true at home, at work and in the church.  Truth will always ultimately win and lies will ultimately fail, so stop thinking about gaining short term advantages.  Speak truth: it will be validated in the long term and demonstrate that you belong to Jesus.