Hastings' Dictionary of the Bible (1898)
SANCTIFY is to prepare or set apart persons or things to a holy use. Ex 13:2. The term "sanctification," when applied to men, denotes the effect of God's Spirit upon the soul. It comprehends all the graces of knowledge, faith, love, repentance, humility, etc., and the exercise of them toward God and man. 2 Thess 2:13; 1 Pet 1:2.
It is a process by which the soul is cleansed from the pollution and delivered from the power of sin, and at the same time endued with those spiritual graces above named, without which there could be no taste or fitness for the joys or employments of the heavenly world. Heb 12:14. Sanctification is the fruit of union to Christ by faith, and it is in the knowledge and belief of the truth as it is in Jesus that the soul becomes the subject of the sanctifying influences of the Spirit. John 17:17. From this inward sanctification proceeds every good word and work. Tit 2:11-14.
When Christ speaks of sanctifying himself, John 17:19, it is in allusion to the law which required the sacrifice to be set apart to a holy use. He separates or dedicates himself as a sacrifice to God for them.