John 17:17-Sanctify them through thy truth: thy word is truth.
Sanctify=hagiazó in the greek. To set apart for God' service.
The Word of the Lord is the final authority where "truth" is concerned.
God has set a standard in His Word in which He commands us to not go beyond, but heed and daily apply to our lives.
We are reminded of 2 truths in this text. (1) The Word of God is the truth that we ALL must be sanctified by for there is no other way to be set apart for God's service apart from His Word which is truth.
(2) The Word of God is truth. Believing or attempting to believe that sanctification is done any other way than through the Word of God is a lie. God's word is final authority, even if man chooses to willfully disobey it.