To say that God is holy means that He is absolutely distinct, transcendent, and morally pure, standing infinitely apart from all creation as the perfect standard of all goodness. Because He is holy, He demands that His people be set apart to Him, reflecting His nature in their worship and daily walk.
The holiness of God is not merely one attribute among many; it is the quality that defines His very essence. As affirmed in the 1689 LBCF Ch.2 §2, God is the 'alone fountain of all being' and is 'most holy in all his counsels, in all his works, and in all his commands.' He is not contingent upon the creation, nor does He derive His worth from it. Rather, as the Westminster Larger Catechism Q.7 describes, He is 'infinite in being, glory, blessedness, and perfection.' His holiness means He is essentially separated from all impurity and is the unique, uncreated source of all moral excellence.
God's holiness dictates the life of His people. In the Old Testament, the distinctions between clean and unclean served as a graphic shadow of this reality, reminding Israel that they were to be set apart from the corruption of the world. As Jehovah says in Leviticus 11:44-45, 'For I am Jehovah your God: sanctify yourselves therefore, and be ye holy; for I am holy.' We are reminded that we are more sinful than we ever dared believe, yet because of the work of Christ, we are invited to walk in the light of His holiness, being renewed after the image of God as we grow in grace.