Ninth Commandment: 16 “You shall not give false testimony against your neighbor. (Exodus 20:16; Dt. 5:20).
5 An honest witness does not deceive, but a false witness pours out lies. (Prov. 14:5)
19 For out of the heart come evil thoughts—murder, adultery, sexual immorality, theft, false testimony, slander. (Matthew 15:19)
(Ex. 20:16: לֹֽא־תַעֲנֶ֥ה בְרֵעֲךָ֖ עֵ֥ד שָֽׁקֶר׃ ס); (Dt. 5:20 לֹֽא־תַעֲנֶ֥ה בְרֵֽעֲךָ֖ עֵ֥ד שָֽׁוְא׃ ס )
Note: that while the English translation is the same, there is a difference in Hebrew.
Exodus speaks of not lying or being untrue; Deuteronomy speaks of being insincere, deceitful- a slight difference in emphasis.
While this law was intended for court, there is an attidue toward false speech that applies very much to every day life. God does not lie, for God does not need to lie. A lie is a purposeful delusion of relaity (which is what "deception" means). God wants us to see reality for what it is. Perhaps some feel that the truth is too painful to bear. Or that we can elevate our own welfare more if we lie.
Prayer: Give me grace to see life for what it is. Give me grace to speak about reality truly yet with love.
Westminster Shorter Catechism:
The ninth commandment requires the maintaining and promoting of truth between man and man, and of our own and our neighbor's good name, especially in witness bearing.
The ninth commandment forbids whatever is prejudicial to truth, or injurious to our own or our neighbor's good name.