Jesus knows who He is. Jesus knows that God sent him to redeem the world. Jesus knows he will pay the price.
Jesus relies on His Father in everything He does. God Himself gave witness. It is God’s work, that He accomplishes that is Jesus’ additional witness. God, the work God gave Him and the Holy Spirit all bear witness to who Jesus is.
We can trust what Jesus says to us. It comes directly from our heavenly Father.
If I were simply speaking on my own account, it would be an empty, self-serving witness.
~~Jesus (John 5:30-33 The Message)