The Mosaic author wrote this about God’s holiness, and how God, or Yahweh (God’s Covenantal name for his people) desires us to relate with him:
Then the Lord spoke to Moses, saying:
2 “Speak to all the congregation of the sons of Israel and say to them, ‘You shall be holy, for I the Lord your God am holy. – Leviticus 19:1,2
And then the Apostle Peter reiterated this command when he wrote this:
14 As obedient children, do not be conformed to the former lusts which were yours in your ignorance, 15 but like the Holy One who called you, be holy yourselves also in all your behavior; 16 because it is written, “You shall be holy, for I am holy.” – 1 Peter 1:14-16
Obviously this is a serious topic! As such we will spend our time this fine Monday considering what this might mean for us as God’s saints here and now in the 21st century. Instead of doing a typical exegetical or expositional analysis of the texts that we have in Leviticus and Peter, what we will do today is attempt to understand what it means, theologically, to be holy. So what we will be doing today is engaging in what the theologians call ‘theological-exegesis’ of the text (by the way, ‘exegesis’ is a Greek word transliterated into English which simply means to ‘interpret out of’, so we will try to press into the theological implications of what the Mosaic and Petrine authors are commanding of us as followers of the only true and living God).
To help us along today, let me refer our attention to a really helpful insight about what ‘being holy’ involves for the Christian. John Webster, one of my favorite bible teachers and theologians, writes:
As we approach the topic, it is imperative that we keep in mind two basic requirements for thinking Christianly about God’s holiness. The first is that we need to understand that theological thinking about holiness is itself an exercise of holiness. Theology is an aspect of the sanctification of reason, that is, of the process in which reason is put to death and made alive by the terrifying and merciful presence of the holy God. Without sanctification – without being caught up by God and cleansed for the service of God in the fellowship of the saints – the work of theological reason is profitless. The second requirement for thinking Christianly about the holiness of God is that we need to make sure that we are thinking about the true God, and not about some God of our own invention. Theological talk of the holiness of God stands under the same rule as all theological talk, namely, that it is truthful only to the extent that it attempts to follow the given reality of God. That given reality is God’s glorious and free self-presentation as Father, Son and Spirit, the Holy One in our midst, establishing, maintaining and perfecting righteous fellowship with the holy people of God.
Let’s break this down a bit, shall we?
1) Being holy cannot come from ourselves, and cannot be realized without God initiating the process of becoming holy with the holiness of his life. So we are called to, as the Apostle Paul calls us for as well, reckon ourselves ‘dead to sin and alive to Christ.’ What lies behind this is the idea that the ‘set apartness’ (or ‘holiness’) that we have been summoned to is not something we can generate in and from ourselves; it is something that is alien to us, and thus we must rely upon God to do the real work of making us holy as he brings us into a participatory relationship with him and his holy Triune life of Father, Son, and Holy Spirit.
2) This second point somewhat picks up where we left off in our last point; the idea that the only way for us to truly ‘be holy’ is if we are aligned in relationship with the only true God who has revealed himself to us in and through Jesus Christ as Father, Son, and Holy Spirit (what we call the ‘Trinity’). This of course is probably the most important realization about holiness that we might be confronted with. Only the Christian God has the resources to make us truly holy; only the Christian God has the power to make us holy; only the Triune God can ask us to be holy and at the same time command us not to look at ourselves in this process (unlike other gods of other religions). He alone can command this of us because he alone has the capacity in himself to be this for us, and to give us, by the Holy Spirit in and through the resurrection of Jesus, the power to live from his yes for us, to live in his holiness and to grow deeper into what it means to be truly ‘set apart’.
3) A function of this, as Peter, and the Mosaic author make clear, is obedience. Under the old covenant (i.e. Leviticus), the people had a whole moral code to follow in order to experience and participate in the holiness of Yahweh that God had called them to. Similarly, Peter emphasizes obedience to God as the mechanism that will allow for us to experience holiness (purity, set apartness, etc.) in our daily lived lives. What is interesting between the time of Leviticus and Peter, though, of course, is that the ‘shadows’ of Leviticus and the Mosaic ‘cult’ have become the ‘substance’ in Jesus Christ. All of these codes and laws the people were to be obedient to in order to experience God’s holiness in their lives really only drove the nail deeper into their hearts making them realize that they had hard heads, and hard hearts, thus pointing them back to Yahweh once again (see Galatians 3 and the role that the holiness-codes were to play in pointing people to Jesus). What happened, of course, is that by time we hear from the Apostle Peter, Jesus, Yahweh in the flesh had come and he had lived the obedient life for us; he lived the life of obedience that we never could, and he lived it to the point of death, resurrection, and ascension. So when Peter calls us to be holy (reiterating and even quoting Leviticus), when he calls us to obedience, he does so with the full knowledge that we have the capacity to do this and experience this as we live from Jesus’ obedience for us by the power of the Holy Spirit in our lives.
I wish we had more time to delve deeper into this most important topic for our daily lives. But as you reflect on this topic throughout the week I would ask you to consider the fact, that as Webster has pointed out, that even thinking about what it means to be holy before God is an act of holiness in and of itself. It is an act and confession of faith that you are beginning to think in ways you never would have lest the holiness of God’s life had already broken into your sinful life and shed abroad in your heart his love, his purity and holiness; which then has resulted in you even wanting to think about what it means to be holy, let alone wanting to live a holy life from God’s holiness for you! So through the week, as you engage in this process of being holy, attempt to identify other passages of scripture that talk about God’s holiness (they are throughout the corpus of Holy Scripture), and simply begin to prayerfully meditate upon what you find. And ask the Lord, as you do this, to make you sensitive to him and his holiness in your life, and watch how that might be manifested as you intentionally and prayerfully contemplate all that this means in your daily and often mundane life. And watch how engaging in this process will begin to take even the mundane, even as it did for the Israelites, into the holy of holies of God’s life for you.
 John Webster, Holiness, kindle loc. 87, 92, 98.