How do we know the ninth commandment is true?

The truth of the ninth commandment is rooted in its divine authority as a command from God, who is Himself the embodiment of truth. The commandment serves a critical purpose: it helps to maintain justice and order in society by requiring honesty, particularly in matters of testimony and reputation. Additionally, the consistency of this moral principle throughout Scripture, from Old Testament teachings to New Testament applications, establishes its truth and importance. Thus, the acknowledgment of God as a God of truth, and the consequential nature of our lies, highlights the necessity of adhering to this command.