What does universal holiness mean in the context of the Day of the Lord?

Universal holiness, as discussed in the context of the Day of the Lord, signifies the total and final sanctification of all believers at Christ's second coming. In Zechariah 14, it describes a time when holiness will be the defining characteristic of God's people, a promise rooted in the complete work of redemption accomplished by Christ. This transformation will result in the removal of sin, and believers will be fully conformed to the image of Christ, existing in perfect communion with God. The passage indicates that holiness unto the Lord will be evident not just in believers but throughout the entirety of creation, marking the establishment of God's eternal Kingdom where sin and its effects are no more.