Michael F. Bird – Evangelical Theology, Second Edition: A Biblical and Systematic Introduction (pp. 629-633). Zondervan Academic. Kindle Edition.

Theosis, also called “deification,” identifies salvation as becoming like God and sharing in the divine nature. In recent years there has been a surge of scholarly interest in theosis in what might be called a rediscovery of the Eastern Orthodox tradition. The Eastern church has had the most interest in theosis as a theological category for salvation. As for a definition of theosis, the Orthodox Study Bible describes it as follows: 

“This does not mean we become divine by nature. If we participated in God’s essence, the distinction between God and man would be abolished. What this does mean is that we participate in God’s energy, described by a number of terms in scripture such as glory, love, virtue, and power. We are to become like God by His grace, and truly be His adopted children, but never become like God by nature. . . . When we are joined to Christ, our humanity is interpenetrated with the energies of God through Christ’s glorified flesh. Nourished by the Blood and Body of Christ, we partake of the grace of God—His strength, His righteousness, His love—and are enabled to serve Him and glorify Him. Thus we, being human, are being deified.”

There is ample scriptural basis for theosis. We read in 2 Peter, “He has given us his very great and precious promises, so that through them you may participate in the divine nature [theias koinōnoi physeōs], having escaped the corruption of the world caused by evil desires” (2 Pet 1:4). Paul states that the purpose of divine predestination is so that believers will be “conformed to the image of his Son” (Rom 8:29). Paul also wrote, “We all, who with unveiled faces contemplate the Lord’s glory, are being transformed into his image with ever-increasing glory, which comes from the Lord, who is the Spirit” (2 Cor 3:18).53 John’s Gospel makes repeated references to believers remaining or dwelling in Christ and to Christ remaining or dwelling in them (John 15:4–9). Johannine salvation can be summed up like this: “I in them and you in me—so that they may be brought to complete unity” (John 17:23). These biblical texts refer to a transformation of believers that brings them into a type of unity, in some mysterious sense, with Christ and God. This is certainly the ingredients for a doctrine of theosis or something like it. 

The concept of becoming united with God and like God was not far from the minds of some church fathers. “Because of his measureless love,” wrote Irenaeus, “he became what we are in order to enable us to become what he is.” Elsewhere he said, “Unless man had been joined to God, he could never become a partaker of incorruptibility,” and later he rhetorically asked, “How can man pass into God unless God has first passed into man?” According to Clement of Alexandria, “The Word of God became man that you may also learn from a man how to become God.” For Origen it was possible to participate in “holiness, wisdom, and divinity itself.” Athanasius memorably wrote that the Word “was made man so that we might be made God.” Augustine declared, “Therefore by joining to us the likeness of His humanity, He took away the unlikeness of our unrighteousness; and by becoming sharer of our mortality, He made us sharers of His divinity.” The First Helvetic Confession sees part of Christ’s priestly office as leading “us into the fellowship of His divine nature.” 

Yet the concept of deification is rather slippery. Is it ontological, relational, or ethical? What precisely is meant by being “made God” or “partake in the divine nature” is not entirely clear. According to Jaroslav Pelikan, “The church could not specify what it meant to promise that man would become divine until it had specified what it meant to confess that Christ had always been divine.” Pelikan adds, “The idea of deification in the Greek fathers had run the danger of obscuring the distinction between Creator and creature.” For Gregory Palamas, theosis is sharing in the communicable divine attributes by immersion in divine energies, whereas Protestants envisage something more like experiencing by grace what is the Son’s by nature, namely, divine sonship. In that case, theosis is a mixture of adoption, infused life, incipient glory, and imitatio Christi. 

Theosis is best conceived as our participation in the Son and transformation into the image of the Son. Deification is, by means of union with Christ, our participation in Christ’s incarnate humanity, its redemptive benefits like adoption, sharing in divine life, a reinstatement of Adamic stewardship of creation, and imitation of the communicable divine attributes—all through the Holy Spirit. So I am happy to use the terms theosis and deification, but I use them only as a shorthand summary for describing how, through Christ’s incarnation and the Spirit’s mediation, believers are transformed to share in the divine life that God bestows in Christ, adopted into Christ’s divine sonship, and are conformed to the pattern of Christ. Anything beyond that is going to raise more problems than it solves. 

Calvin is a particularly helpful resource for considering theosis. Several texts from Calvin appear at first glance to support theosis. Commenting on 2 Peter 1:4, he said, “Let us then mark, that the end of the gospel is, to render us eventually conformable to God, and, if we may so speak, to deify us.” For Calvin deified means to be made “partakers of divine and blessed immortality and glory, so as to be as it were one with God as far as our capacities will allow.” In the Institutes Calvin said, “The flesh of Christ is like a rich and inexhaustible fountain that pours into us the life springing forth from the Godhead into itself. Now who does not see that communion with Christ’s flesh and blood is necessary for all who aspire to heavenly life?” And in their union with Christ, believers are “participants not only in all his benefits but also in himself.” Furthermore, a wondrous exchange sees believers share in what Christ has and is: 

Having become with us the Son of Man, he has made us with himself sons of God. By his own descent to the earth he has prepared our ascent to heaven. Having received our mortality, he has bestowed on us his immortality. Having undertaken our weakness, he has made us strong in his strength. Having submitted to our poverty, he has transferred to us his riches. Having taken upon himself the burden of unrighteousness with which we were oppressed, he has clothed us with his righteousness. 

Calvin’s idea of a transformative and participatory union with God in Christ through the Spirit can be squared with theosis, if one regards believers as participating in God’s energies like divine glory and life (energeia) rather than participating in God’s essence or immanent being (ousia), and if one treats deification as a conflation of adoption, imitation, and glorification. However, if one holds up Calvin to a Byzantine theological standard of theosis with anything remotely ontological, I think he falls short. Of course, it depends on which version of theosis we are talking about—Irenaeus, Clement of Alexandria, or Gregory Palamas. For Calvin, there can be no real or absolute sharing in the divine nature. Calvin’s notion of mystical union with Christ is not a participation in Christ’s hypostatic union or in the triune communion per se but a participation in the incarnate Christ’s union with God as mediated by the Spirit. The benefits of our union with Christ’s humanity as it is united with God are divine sonship, eternal life, and everlasting glory. Yet for Calvin, the Spirit draws us into Christ’s incarnate humanity and its union with God the Father, not into a divine ontology. 

Bruce McCormack rejects the notion that Calvin’s idea of union with Christ can be seriously integrated with a realist notion of theosis. McCormack notes that Calvin’s Christology will not actually allow God’s essential life to be communicated to believers (so as to avoid the error of Andreas Osiander, who taught that we share in God’s essential righteousness in justification). McCormack argues that Calvin has dispensed with that which made deification theories possible, namely, the idea of an interpenetration of the natures. For Calvin, the believer participates only in the human nature of Christ. Since there can be no interpenetration of the natures in Christ, participation in the human nature of Christ cannot result in a participation in the divine nature. One simply cannot find the ontological purchase needed for a hard deification theory in Calvin’s Christology. In my mind, Calvin is at best an advocate of a soft form of deification (i.e., participation in divine life, sonship, and glory), not a radically mystical and metaphysical sense of deification.