Jesus is an ambassador and is seeking the glory of the One Who sent him, not glory for Himself. Note that He does not say that He has the truth or that what He says is true; Jesus says that He is true. (14:6)

John 14:6  Jesus answered, “I am the way and the truth and the life. No-one comes to the Father except through me.

“nothing false” = “no unrighteousness” (KJV) = Jesus probably uses the negative way of stating this as a contrast between Him and the Jews in whom was unrighteousness.

Jesus gives us a test here to prove whether a preacher or a servant of God is really serving God or is instead serving himself. Does he magnify himself or does he magnify God? Does he seek his own glory or does he seek the glory for God? Does the church at which he serves belong to him or does it belong to God?

This test may also be applied to ourselves. Are you seeking the glory of God when you serve Him or do you prefer the praises of men for what you do? There is a danger in serving in a visible capacity, just as there is in God using you to do great things. It is a similar danger to that of increasing your education and intellect. They all can lead to pride. This is not a warning to not do great things for God — but it is a warning to beware lest the enemy uses those great things to your disadvantage. The solution is to always keep your eyes upon Jesus and serve Him with a pure heart, not wanting any glory for yourself, but all for Him. Humility is the most powerful force in the universe. Be sure to keep it in your arsenal at all times!