Sanctify them through thy truth: thy word is truth.
John 17:17, kjv
Sanctification begins in regeneration. The Spirit of God infuses into man that new living principle by which he becomes "a new creature" in Christ Jesus. This work, which begins in the new birth, is carried on in two ways--mortification, whereby the lusts of the flesh are subdued and kept under; and vivification, by which the life which God has put within us is made to be a well of water springing up unto everlasting life. This is carried on every day in what is called "perseverance," by which the Christian is preserved and continued in a gracious state, and is made to abound in good works unto the praise and glory of God; and it culminates or comes to perfection, in "glory," when the soul, being thoroughly purged, is caught up to dwell with holy beings at the right hand of the Majesty on high. But while the Spirit of God is thus the author of sanctification, yet there is a visible agency employed which must not be forgotten. "Sanctify them," said Jesus, "through thy truth: thy word is truth." The passages of Scripture which prove that the instrument of our sanctification is the Word of God are very many. The Spirit of God brings to our minds the precepts and doctrines of truth, and applies them with power. These are heard in the ear, and being received in the heart, they work in us to will and to do of God's good pleasure. The truth is the sanctifier, and if we do not hear or read the truth, we shall not grow in sanctification. We only progress in sound living as we progress in sound understanding. "Thy word is a lamp unto my feet and a light unto my path." Do not say of any error, "It is a mere matter of opinion." No man indulges an error of judgment, without sooner or later tolerating an error in practice. Hold fast the truth, for by so holding the truth shall you be sanctified by the Spirit of God.
-Charles Spurgeon, Morning and Evening Devotionals, Public Domain