One of the great synonyms for "holiness" is "spirituality." In 1 Peter 1:15, the Word of God could say, "Be spiritual, just as the Lord, who has called you, is spiritual; and practice spirituality in all manner of living."
Holiness, the way it should be understood in the Word of God, is so valuable. It means that we sanctify- purify-our lives daily by faith, and then the Word of God is sanctified in us.
So, what does the Word of God mean in Psalm 68:18 where it says that He ascended on high, led captivity captive, and received gifts for men, and for the rebellious also, "that the Lord God might dwell among them"? It means that He overcame our rebellion by inhabiting our soul.
Please remember, the Lord has given us wisdom, righteousness, sanctification, and redemption; and "as it is written, He that glorieth, let him glory in the Lord" (1 Corinthians 1:30-31). God is saying, "Don't you know that because of the gift of grace and the gift of righteousness, I have made you to be wise, righteous, sanctified, and redeemed? You have been totally and completely set apart for My use."