In this context used by Jesus, the words ‘THE TRUTH’ embodies a higher meaning, aside from the obvious meaning of ‘not lying’.  ‘The Truth’ means THE WORD OF GOD.  Jesus proclaims that he is the embodiment of God’s word. This idea is shown in three scriptures:

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(Jesus Prays To God For His Disciples)

John Chapter 17, Verse 15 - 17:

“I do not ask Thee to take them out of the world, but to keep them from the evil one.  They are not of the world, even as I am not of the world.  Sanctify them in the truth; Thy word is truth.”

 

John Chapter 8, Verse 31: 

Jesus therefore was saying to those Jews who had believed Him, “If you abide in My word, then you are truly disciples of Mine; and you shall know the truth, and the truth  shall make you free.”

 

(Jesus Is Questioned By Pontius Pilate)

John Chapter 18, Verse 37:

Pilate therefore said to him, “So You are a king?”  Jesus answered, “You say correctly that I am a king.  For this I have been born, and for this I have come into the world, to bear witness to the truth.  Everyone who is of the truth hears My voice.”