"SANCTIFY THEM BY YOUR TRUTH. Your Word is TRUTH."
John 17:17 (NKJV)
Comment: The Word of God is the truth, and the believers are purified, sanctified or set apart by It.
To be sanctified means to be set apart for a particular purpose.
It is the Word of God that makes holy or clean (1 Peter 1:15,16); It makes you a useable vessel of God (2 Timothy 2:19-21).
The reading and studying of the Word of God sets apart for the purpose of God. The deeper you are in the knowledge of God's Word and the practice of it, the holier, purer, you are (1 Peter 1:1516). And that makes you a prepared and ready vessel for the Use of God:
19 NEVERTHELESS THE SOLID FOUNDATION OF GOD STANDS, HAVING THIS SEAL: “THE LORD KNOWS THOSE WHO ARE HIS,” and, “LET EVERYONE WHO NAMES THE NAME OF CHRIST DEPART FROM INIQUITY.” 20 BUT IN A GREAT HOUSE THERE ARE NOT ONLY VESSELS OF GOLD AND SILVER, BUT ALSO OF WOOD AND CLAY, SOME FOR HONOUR AND SOME FOR DISHONOUR. 21 THEREFORE IF ANYONE CLEANSES HIMSELF FROM THE LATTER, HE WILL BE A VESSEL FOR HONOUR, SANCTIFIED AND USEFUL FOR THE MASTER, PREPARED FOR EVERY GOOD WORK" (2 Timothy 2:19-21 NKJV). Peace.