You can tell the truth in this world and the people of the world can deny seeing the truth. Why don’t they see the truth like we do? Perhaps they like what lies that feed the flesh and not things of God. The world follows a false god. We as Christians follow the truth from the living God having the Holy spirit to guide us and lead us in truth.
Psalms 33:4KJV
For the word of the LORD is right; and all his works are done in truth.