A witness should be truthful because he knows the truth.
When you bear false witness you are putting a thought in someone’s mind.
Matthew 15:18 You speak what is in the heart.
How many people carry sword scars from those that bear false witness?
Matthew 26:60, Proverbs 14:5
A faithful witness will not lie.
Proverbs 19:5 A false witness shall not be unpunished.
What is our motive?