God certainly puts a high premium on truth. If we are to be imitators of Him, we must prize the truth as well (Eph. 5:1). Scripture calls our Creator the "God of truth" because truthful speech and actions are particularly characteristic of Him (Isa. 65:16). All men are liars, but "of a truth God will not do wickedly" (Job 34:12; see Ps. 116:11). Worship is unacceptable to Him unless it is conducted "in spirit and truth" (John 4:24). Moreover, the incarnate Son of God, our Lord Jesus Christ, refers to Himself as the truth (14:6).
Due to the close association of God and truth in Scripture, it is not surprising that we would find a law that emphasizes the importance of truth in the Ten Commandments, which is an extended summary of the Lord's will for humanity. The ninth commandment is the law of which we speak, and it is found in today's passage and covered in question and answer 112 of the Heidelberg Catechism.
This statute is popularly remembered as "thou shalt not lie," and lying is forbidden in this commandment. That is not all the statute addresses, however, and we see this as we consider the actual phrasing of the law in its context. The immediate concern of the ninth commandment is legal testimony. Because human beings are sinners and inclined to tell falsehoods about others in order to advance their own positions or standings, God's law deals with false witnesses quite strongly. Deuteronomy 19:15–21 regulates witnesses in the setting of a formal hearing before a judge in ancient Israel. Anyone found guilty of bringing false testimony against a neighbor was to be inflicted with the same punishment that the false witness hoped to inflict on his neighbor. Knowing that one might receive the penalty he hoped to impose on another through false testimony was a powerful motivation for a witness to be honest during legal proceedings.
This connection with causing harm through legal testimony tells us that the ninth commandment bars us from committing any act that might bring undeserved suffering on another person. The focus is on our speech, but not exclusively. Words and deeds that unjustly destroy others' reputations, harm them in court, or otherwise promote evil and falsehood are prohibited by the ninth commandment.
There are a number of different ways in which we can break this rule against false witness. If we teach or proclaim wrong things about God’s character, we are bearing false witness. If we gossip and backbite to destroy how a person is viewed in the eyes of others, we are bearing false witness. Ultimately, if we do not prize truth as highly as the Lord does, we will find it easy to break the ninth commandment. Let us, therefore, aim for truth in all our speech.