Sanctification: Separated Unto Him

Hebrews 10:
10 And by that will we have been sanctified through the offering of the body of Jesus Christ once for all……….. 

14 For by a single offering he has perfected for all time those who are being sanctified. 

Sanctification is not a "process". It is not a progressive improving of myself. It is not the working out of which Paul speaks in Philippians 2:12-13. It is not the good works we are predestined for. (Ephesians 2:10) All of these things the saints do as they have been both justified, (redeemed), and sanctified, (set apart), for these works.
Therefore, sanctification is simply defined as our being "set apart" in Christ, who is Himself set apart from all things.

Hebrews 7:
26 For it was indeed fitting that we should have such a high priest, holy, innocent, unstained, separated from sinners, and exalted above the heavens.
27 He has no need, like those high priests, to offer sacrifices daily, first for his own sins and then for those of the people, since he did this once for all when he offered up himself. 

John 17:
14 I have given them your word, and the world has hated them because they are not of the world, just as I am not of the world.
15 I do not ask that you take them out of the world, but that you keep them from the evil one.
16 They are not of the world, just as I am not of the world.
17 Sanctify them in the truth; your word is truth.
18 As you sent me into the world, so I have sent them into the world.
19 And for their sake I consecrate (sanctify; kjv) myself, that they also may be sanctified in truth.
20 "I do not ask for these only, but also for those who will believe in me through their word,
21 that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me.

The Lord said "be holy (altogether separate) as I am holy (altogether separate)". He did not say be perfectly sinless, as I am perfectly sinless. He has perfected once for all and for all time those "being sanctified", that is those are elected (predestined to), and called to, justification and sanctification. Just as He is separate (sanctified) from all things in His own inherent perfection, He has perfected all who are His, to be sanctified from all things in Christ, in the world, but not part of it.
Once again, the scriptures do not speak of a process of improvement. The Savior needs no assistance in accomplishing that which for which He came. We are holy for the very reason that He has declared us to be so. As the song says; some days are diamonds, and some days are stones, some days we do better than others. However, Scripture tells us that for the saints, everyday is a day of growing in grace and knowledge of Him.

Hebrews 4:
14 Since then we have a great high priest who has passed through the heavens, Jesus, the Son of God, let us hold fast our confession.
15 For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin.
16 Let us then with confidence draw near to the throne of grace, that we may receive mercy and find grace to help in time of need. 

1Thess 5:
23 Now may the God of peace himself sanctify you completely, and may your whole spirit and soul and body be kept blameless at the coming of our Lord Jesus Christ.
24 He who calls you is faithful; he will surely do it. 

Philippians 1:6 And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ. 

Hebrews 9:
27 And just as it is appointed for man to die once, and after that comes judgment,
28 so Christ, having been offered once to bear the sins of many, will appear a second time, not to deal with sin but to save those who are eagerly waiting for him. 

Ephesians 1:
3 Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places,
4 even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love
5 he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will,
6 to the praise of his glorious grace, with which he has blessed us in the Beloved.
7 In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace,
8 which he lavished upon us, in all wisdom and insight
9 making known to us the mystery of his will, according to his purpose, which he set forth in Christ
10 as a plan for the fullness of time, to unite all things in him, things in heaven and things on earth.
11 In him we have obtained an inheritance, having been predestined according to the purpose of him who works all things according to the counsel of his will,
12 so that we who were the first to hope in Christ might be to the praise of his glory.
13 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit,
14 who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.

The Holy Spirit comes as the guarantor, i.e. earnest deposit, that all that Christ has fulfilled through his life, death, and resurrection will be consummated in time upon His return, at the “end”, of the end of the ages. He is not our guide to a “better us”. How much better does one need to be when one has already been freely justified, sanctified, and baptized into both His death and resurrection?
Fulfillment and consummation-
It is finished!