Humanity was meant for something more than its current state. Those of us who are in Christ are, by the grace of God, slowly being transformed into that something more. We are being made like God. This is the essential nature of the process of sanctification: slow transformation from our current state into the image of God. Sanctification is one of the most important ideas in the Bible, and many things besides people were sanctified in the course of salvation history. Sanctification is being set apart for service to God, being made “holy” —including especially the various elements used in the pre-Christ sacrificial system. This kind of holiness entails both moral uprightness and distinction from the mundane.

We first recognize that moral failure is a reality—a sad and tragic reality, but a reality nonetheless—in the life of the Christian. Even after experiencing regeneration and justification, we remain simultus justus et peccator, to borrow Luther’s famous phrase: simultaneously justified and yet sinners. We remain in the world and of the world, rather than in it but not of it. We are not yet wholly set apart for God’s works, but too often continue to pursue fallen ends via fallen means. We need to be transformed so that we pursue God’s ends (ultimately: God himself) as he has called us, rather than the things of the earth.

But God in his wisdom has ordained that we grow into this. We are justified at a single moment by faith in Christ, and our sanctification will ultimately be finished in a single moment when we are glorified upon our death. In the interval, though, God has called us to pursue him, to strive for the holiness which Christ exemplified for us. As we do, we learn to trust him more and rely more thoroughly on his power and wisdom rather than our own, and this too is part of the process of sanctification. When we are perfected, it will not be a matter of suddenly being able to do on our own what we could not before, but rather that we will finally depend wholly on God.

In this we are growing into the full maturity of humanity. Our model is Jesus Christ: the God-man who shows us what it means to be a perfect human being. He taught us over and over again not only by example but by direct affirmation that his life was characterized above all by dependence on his Father and that he acted not on his own power but that of the Spirit. In our sanctification, we learn to walk the same way. As in our justification, this comes about because we are being united to Christ by the indwelling Spirit—so our growing humanity is also growing to participate in the life of the Trinity. We pursue the Father and his ways, empowered by the Spirit to partake of Christ’s risen, divinized humanity.

This way of putting it is often jarring to western theologians, but is fully orthodox and has been part of the Eastern Orthodox tradition for sixteen centuries and more. It draws directly on the language of 2 Peter 1:4, which reminds us that we are partakers of the divine nature. It was on that very basis that Peter laid out his enjoinder to grow in the various measures of sanctification: faith, virtue, knowledge, self-control, steadfastness, godliness, brotherly affection, and love (a list that bears what is surely not a coincidental similarity to Paul’s fruit of the Spirit). Sanctification is our wholehearted pursuit of the things of God, not on our own power but by his gracious work in us, until we someday attain to full maturity and depend wholly on the Spirit’s uniting us to Christ.