Truth of which we are speaking, is:

• The one that Christ personifies "I am the Truth" (JOHN 1:17)
• and something that he brought. "Grace and truth came through Jesus Christ" (JOHN 14: 6)

The Apostle Paul tells us about the truth that is in Christ, and not what we believe as "our truth"; We can believe that our reasoning and intentions are true. But if they are not based on Truth in Christ, they are vulnerable to any attack.
Jesus for some reason told us that He was the Truth.