Good question. I understand you’re asking for a reason why it’s wrong to lie and not just a source such as “Distance yourself from falsehood (Ex. 23:7).” But before we answer this question of why tell the truth and not lie, let me ask another question. Why are we here? Why is there a world?
This question is asked by Rabbi Moshe Chaim Luzzatto in The Way of God, and is also addressed by Rabbi Yosef Karo in Maggid Mesharim. The gist of what they say is the following: The purpose of Creation is kindness. God wants to bestow the greatest possible good upon us. The ultimate and greatest good is God Himself, and therefore, the ultimate good is closeness to God. Closeness to God requires compatibility and similarity to God. For this reason, human beings must have free will (i.e., God acts because He chooses to do so, not because He is coerced).
Therefore, we must be in a world in which there is choice so that we can try to be as "Godlike" as possible. The good has to be internal, not external, just as God is intrinsically good. The only way to internalize and be intrinsically good is to do it through challenge and free will, and therefore this world was created.
