Exodus 20:16 (ESV)
You shall not bear false witness against your neighbor.
Some people believe that lying is only a problem if you really hurt someone--or if you get caught. But God doesn't see it that way. God cares about the truth because our relationships depend on it. Like God, Christians believe that honesty is very important.
Of course, being honest is not the same as saying everything you think. If you don't like something, or you believe a comment someone made is pretty foolish, you don't necessarily have to say so. There are also times when telling the whole truth can cause too much hurt.
I remember reading about people who hid Jews from harm in World War II and lied about it when German soldiers asked them. In that situation, the effect of deception was more in line with God's intention for relationships and caring for others.
But rare exceptions shouldn't blind us to God's basic demand for honesty in relationships. If I am going to relate to you in a loving way, I need to be able to count on you for the truth. If I can't, I will feel manipulated, become suspicious, distrust your word, and eventually become alienated from you.
Lying changes more than the facts; it also changes the liar. If I lie to you, I erode our relationship, whether or not you know I lied. Lying to God does the same thing. The only difference is that God already knows.
Dear Lord, even though we may be solidly against outright lies, it's hard at times not to be deceptive. Help us to honor others with honesty and to speak the truth in love. In the Name of Jesus, Amen.