Christians celebrate throughout the year a number of holy days, each of which emphasizes the life and work of Jesus. Of notable importance are Christmas, the commemoration of the Son’s entrance into the world whereby he takes on our humanity through the incarnation, and Easter, a celebration of Christ’s death and resurrection. In liturgical traditions from both the East and West, Christians also celebrate Ascension Day, which commemorates Jesus’s ascension to heaven.

Ascension Day is one of the earliest Christian celebrations. Tradition states that it is apostolic in origin and dates back to as early as the first century. According to Scripture, after the events of his death and resurrection, Jesus appeared to his followers over a span of forty days (Acts 1:3) and then was taken up into heaven to sit at the right hand of the Father (Mk 16:20; Lk 24:53; Acts 1:9). Christians, therefore, celebrate Ascension Day on the fortieth day after Easter Sunday.

Jesus’s ascension remains an essential teaching of the Christian church. As with the incarnation, death, and resurrection of the Son of God, the ascension is intricately connected to our salvation. Each should be taken as part of the seamless and inseparable work of Christ, as demonstrated in the writings of the early church.

In his defense of the incarnation, Athanasius (c. 297 C.E. – 373 C.E.), the Bishop of Alexandria, remarked that “it was our sorry case that caused the Word to come down” (Athanasius, On the Incarnation, 1.4). Death had dominion over us because of sin, and it was only through the incarnation of the Word that God could put an end to death and corruption. The Word, who is immortal and who is also the Father’s Son, is incapable of dying. “For this reason,” claimed Athanasius, “He assumed a body capable of death, in order that it, through belonging to the Word Who is above all, might become in dying a sufficient exchange for all, and, . . . put an end to corruption for all others as well, by the grace of the resurrection” (Athanasius, On the Incarnation, 2.9). Toward the latter part of his work on the incarnation, Athanasius says something startling: the Word “assumed humanity that we might become God” (Athanasius, On the Incarnation, 8.54). This may sound strange to our modern ears, but Athanasius’s claim would have made perfect sense among his Greek hearers. It is not that humanity becomes God in an ontological sense, as one might find in pantheism. For Athanasius and the other Greek Fathers, a clear distinction remains between God and creation. God alone is eternal, immortal, uncreated, and incorruptible. Rather, his point was that through the work of the Son of God we become a “holy race” and “partakers of the Divine Nature” (Athanasius, Letter 60, to Adalphius, 4; cf. 2 Peter 1:4). God, by his grace, shares eternal and abundant life with his creatures.

By no means was Athanasius the only church Father to emphasize this teaching that we now call “theosis” (deification). It first appeared in the work of Irenaeus, who claimed that God became incarnate through the Son in order to “win back to God that human nature (hominem) which had departed from God” (Against Heresies, 3.10.2). The doctrine of theosis places emphasis on restoration. Not only was Christ’s work for the forgiveness of sin and for our reconciliation to God; it was also for the restoration of our fallen humanity, for our healing, and to bring us into union with God. Theosis, then, refers to the full saving work of God in our lives, which ultimately culminates in our glorification and immortality.

Jesus, who is our advocate and intercessor before the Father (1 Jn 2:1), and who sympathizes with us in our suffering (Heb 2:17-18), experienced the full weight of our humanity while on earth (Heb 2:10-18; 4:15; 5:7-10). Yet, he did so without sin (1 Pet 2:22; 2 Cor 5:21; Heb 4:15; 1 Jn 3:5). He went before us and is now present with the Father. Because of the completed work of Christ we too may share in the full restoration of our humanity and in our future glorification (Rom 8:18). Not only do we experience forgiveness and a relationship with God, our bodies also will be raised in the likeness of Jesus’s resurrected body—mortality has been clothed with immortality (1 Cor 15:54). Jesus’s resurrection and ascension gives us the ultimate hope and assurance that God has defeated death. One day, those who are in Christ will bask in the indwelling and glorious presence of God in the renewed heavens and earth (Rom 18:21; Rev 21:1-3).