Exodus 31:13 Speak thou also unto the children of Israel, saying, Verily my sabbaths ye shall keep: for it is a sign between me and you throughout your generations; that ye may know that I am the Lord that doth sanctify you.
Jehovah Mekoddishkem; the Lord that sanctifies you.
This is the biblical etymology of sanctification according to the ISB encyclopedia:
“The root is found in the Old Testament in the Hebrew verb qadhash, in the New Testament in the Greek verb hagoazo. The noun “sanctification” (hagiasmos) does not occur in the Old Testament and is found but 10 times in the New Testament, but the roots noted above appear in a group of important words which are of very frequent occurrence. These words are “holy,” “hallow,” “hallowed,” “holiness,” “consecrate,” “saint,” “sanctify,” “sanctification.” It must be borne in mind that these words are all translations of the same root, and that therefore no one of them can be treated adequately without reference to the others. All have undergone a certain development. Broadly stated, this has been from the formal, or ritual, to the ethical, and these different meanings must be carefully distinguished.”
The action of sanctification is separation. That action varies in definition by who is responsible for the separation and by what is being set aside. There is God’s part, His actions, and then there is our part, our actions. We can be seen by God from His point of view in what He has done on His part. We, on the other hand, might not see it that way because we have not done out part.
1 John 1:8-9 If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
From God’s point of view it is unnecessary but from ours it is desperately needed. This will cleanse our conscience and keep us moving in the right direction.
Keeping the Sabbath is but a sign and only a sign. Some day we will explore exactly what that means.