Sanctification is a state of separation unto God; all believers enter into this state when they are born of God.
Sanctification is the same Greek word as holiness, “hagios,” meaning a separation. First, a once-for-all positional separation unto Christ at our salvation. Second, a practical progressive holiness in a believer’s life while awaiting the return of Christ. Third, we will be changed into His perfect likeness—holy, sanctified, and completely separated from the presence of evil.
Saints are 'Sanctified ones'.
Psalm 4:3 But know that the LORD has set apart the godly for himself; the LORD hears when I call to him.
(17) Therefore go out from their midst, and be separate from them, says the Lord, and touch no unclean thing; then I will welcome you,
(18) and I will be a father to you, and you shall be sons and daughters to me, says the Lord Almighty."
God sets us apart with a promise that He will be our father and we shall be His sons and daughters. We should live in obedience as those set apart for service unto Him.