The word "sanctification" derives from the Latin noun "sanctificio". This original Latin word means "to separate and set aside" (source).
To me, this rings of Isreal being set aside as God's holy people. (As seen in Deut. 7:6-8 and Leviticus 20:26) Also, it seems to reverberate in the New Testament with Jesus' words in the gospel of John.
John 17:16 (NIV)
16 They are not of the world, even as I am not of it.
Sanctification, in this sense, is to be set apart from the world--to be a different people.
However, this original Latin word was actually translated from Greek. It's not actually the source word. The original Greek word is often translated into English as "wash" or "cleanse".
This implies that we are to be washed of our sins.
There's an excellent use of this in Ephisians 5:25-26. The NIV translates this as "cleanse"
Ephisians 5:25-26 (NIV)
25 Husbands, love your wives, just as Christ loved the church and gave
himself up for her 26 to make her holy, cleansing her by the
washing with water through the word
However, the original King James uses the word "sanctify"
Ephisians 5:25-26 (KJV)
25 Husbands, love your wives, even as Christ also loved the church, and gave himself for it;
26 That he might sanctify and cleanse it with the washing of water by the word
This cleansing from sin can also be seen in the Old Testamant.
Leviticus 16:30 (KJV)
30 For on that day shall the priest make an atonement for you, to
cleanse you, that ye may be clean from all your sins before the LORD.
It should be noted, though, that the translation of "sanctify" in the Old Testament didn't suffer from this same duality of definition. It's just an example of how God's holy people should be both "set apart" and "cleansed".
So, there is kind of a two-fold definition. My source article puts it well:
- In position believers are eternally set apart for God by redemption and are positionally, therefore, holy and righteous from the moment of believing.
- In experience the believer is being sanctified by the work of the Holy Spirit and scripture.
(emphasis in the original)