"But we are bound to give thanks to God always for you, brethren beloved by
the Lord, because God from the beginning chose you for salvation through
sanctification by the Spirit and belief in the truth." 2 Thessalonians 2:13

Sanctification: simply stated is growing in holiness.
The Illustrated Dictionary of the Bible, Herbert Lockyear, Sr. Editor says,
It is "the process of God's grace by which the believer is separated from
sin and becomes dedicated to God's righteousness."

Sanctification is produced--
By God:
"Now may the God of peace Himself sanctify you completely; and may your
whole spirit, soul, and body be preserved blameless at the coming of our
Lord Jesus Christ." 1Thessalonians 5:23

By Christ:
"For both He who sanctifies and those who are sanctified are all from one
Father; for which reason He is not ashamed to call them brethren."
Hebrews 2:11

By The Holy Spirit:
In the Apostle Peter's first letter we see,
"Peter, an apostle of Jesus Christ, to those...who are chosen according to
the foreknowledge of God the Father by the sanctifying work of the
Spirit..." 1 Peter 1:1-2

By Truth and the word:
Jesus prays to the Father,
"Sanctify them in the truth; Thy word is truth." John 17:17
And Vs. 19,
"And for their sakes I sanctify Myself, that they themselves also may be
sanctified in truth."

"Sanctification is based on the sacrificial death of Christ." (Ibid),
"...Just as Christ also loved the church and gave Himself for it, that He
might sanctify and cleanse it with the washing of water by the word, that
He might present it to Himself a glorious church, not having spot or
wrinkle or any such thing, but that it should be holy and without blemish."
Ephesians 5:25-28

Believers also have a responsibility in the process of growing in
sanctification.
We are to be holy:
"But as He who called you is holy, you also be holy in all your conduct,
because it is written 'Be holy for I am holy.'" 1 Peter 1:15-16

Jesus said in Matthew 5:48,
"Therefore you are to be perfect, as your heavenly Father is perfect."

In directing the Thessalonians, Paul says,
"For this is the will of God, your sanctification; that you should abstain
from sexual immorality; that each of you should know how to posses his
own vessel in sanctification and honor, not in passion or lust, like the
Gentiles who do not know God." Thessalonians 4:3-5

We must walk in the Spirit'
"...Walk in the Spirit, and you shall not fulfill the lust of the flesh. For
the flesh lusts against the Spirit, and the Spirit against the flesh; and
these are contrary to one another." Galatians 5:16-17

If we walk in the Spirit then the Fruit of the Spirit shall be manifested
which is,
"...Love, joy, peace, longsuffering, kindness, goodness, faithfulness,
gentleness, self control. Against such there is no law." Galatians 5:22-23

There is so much more concerning sanctification in Scripture and it is my
hope that each will be led to do a personal study. You will come to know
the Lord in a way that will bring joy to your heart.

I will close with 1 Thessalonians 5:23 from The Amplified Bible,
"And may the God of peace Himself sanctify you through and through [separate
you from profane things, make you pure and wholly consecrated to God]; and
may your spirit and soul and body be preserved sound and complete [and
found] blameless at the coming of our Lord Jesus Christ (the Messiah)."

Thank you most Holy God; Father, Son and Holy Spirit for the great love with
which You love us. The love that sets us apart for holiness, purity,
redemption, reconciliation, completeness. Our sanctification is on going day
to day as we grow in holiness, but all will be perfect in Your presence in
eternity. We praise, adore and honor You. Amen