In considering how the theme of holiness is developed in the old covenant and fulfilled in the new, it is important for us to define holiness with more precision. Typically, we associate holiness with purity of intent and deed, and, given the teachings of our Savior, such things are certainly part of what it means to be holy (Mark 7:14–23). Still, we should note that moral purity is more a consequence of holiness than holiness itself. According to the way the word is used in Scripture, holiness, in its most fundamental sense, refers to that which is set apart for the Lord’s use. Objects that in themselves are morally neutral, such as clothing, can be holy because they are dedicated to God’s service (Ex. 31:10). Thus, inherent moral purity is not necessary for a created object to be considered holy, at least when we are talking about inanimate objects. Created things can be declared holy before they are really pure.
The idea that something unholy can be declared holy is foundational to understanding a Christian’s sanctification (our growth in holiness). When God calls people out from worldliness, He sets them apart as holy (19:1–6). He declares them righteous in Christ, and then, in response, they are led by His Spirit to actually become holy over the course of their lives. Being declared pure, they strive toward purity. The great tragedy of the old covenant — and even the new covenant, to a degree — is that not everyone in the visible church actually lives up to the declaration that God has pronounced over His people. People under the old covenant forgot God’s commands just as people in the new covenant church forget and thus fall into sin. For some, this is but a temporary lapse, and they are restored by repentance (Ps. 51). With others, the amnesia is permanent because they professed faith without possessing it, never truly knowing the ramifications of what it means to be declared holy.
The nation Israel, as the old covenant community, included many who never grasped God’s declaration and call of holiness (Rom. 9:6). The prophets looked forward to a day when the Lord would intervene and pave the way for His people to be holy in both word and deed. This is what the prophet Isaiah longed for as recorded in today’s passage — the day when the “Redeemed of the Lord” would be finally and fully perfected in holiness.
God intervened two thousand years ago to cleanse His people and make them holy, first in His declaration and then in their Spirit-enabled practice. Of course, we still struggle with sin as we wait for this work to be finished. Nevertheless, the call to holiness remains, and we have the Spirit to work in us to this end. Being in Christ, we are given the will to be conformed to His image as citizens of His kingdom.