The Feast of the Ascension commemorates the Ascension of Christ into heaven. There is documentary evidence that this feast has been celebrated at least since the fourth century. St. Augustine says the feast is of apostolic origin. The longest scriptural account of the Ascension is found in our first reading from Acts 1:1-11, and our Gospel is taken from St. Mark's account in Mark 16:15-20. The Latin ascensio signifies that Christ was raised up by his own powers. The Feast of the Ascension ranks with Easter and Pentecost as the most solemn on the church calendar. The feast was originally celebrated as a vigil followed by an octave (the feast day and seven days following it) in anticipation of Pentecost. The feast falls on a Thursday exactly 40 days after the Resurrection of Christ on Easter Sunday. In the US this feast is a Holy Day of Obligation but it has been transferred to Sunday, May 24th.
The importance of this feast flows from its connection to the Paschal mystery. As the Catechism notes the Paschal mystery is fully understood as Christ's passion, crucifixion, death, burial, descent into hell, resurrection and ascension (CCC 512). Thus the ascension is the culmination of the Paschal mystery. In the Second Vatican Council Constitution on Sacred Liturgy the council Fathers note that the purpose of the liturgy is to make present the fullness of the Paschal mystery. The council Fathers point out; "For well-disposed members of the faithful, the liturgy of the sacraments and sacramentals sanctifies almost every event in their lives; they are given access to the stream of divine grace which flows from the Paschal mystery of the passion, death, the resurrection of Christ, the font from which all sacraments and sacramentals draw their power" (SC 61).
Jesus' solidarity with all humanity in the mystery of the Incarnation is brought to completion by the substitution of his own obedience for our disobedience in the Paschal mystery (CCC 615). Because Christ is one person in two natures, everything Christ does as a man is also an act of God. By his glorious ascension, Christ has "opened the gates of heaven to receive his faithful people" (Preface for Easter II). Christ has inaugurated a New Creation (2 Corinthians 5:17) and has become a New Adam (Romans 5:18).
The Fathers of the Church have used different scriptural images to reflect on how this solidarity with Christ takes place. Fathers of the East such as St. Gregory of Nyssa (330-395), and St. John Chrysostom (347-407) used the Old Testament image of the "firstfruits" to explain this mystery. By offering the first of the fruits and the firstborn of the herds and flocks, it was understood that the whole was contained in the part that was offered. St. John Chrysostom observes;
As it happens in a field full of corn, when a man takes a few ears of corn and makes a small sheaf and offers it to God, he blesses the whole cornfield by means of this sheaf, so Christ has done this also, and through that one flesh and firstfruits has made our race to be blessed. But why did he not offer the whole of nature? Because that is not the firstfruits if he offers the whole, but if he offers a little, preparing the whole to be blessed by the smaller amount. (Sermon on the Ascension PG, 50:441-52)
By his bodily ascension into heaven Christ becomes the firstfruits which are accepted as a representative of the whole human race. In effect Jesus becomes the font and origin of ascended and glorified life which comes to us through the Sacraments.
In the West this same truth was highlighted by St. Augustine who emphasized our communion with Christ by meditating on the image of the Body of Christ. St. Augustine comments on the deeper significance of our oneness or communion with Christ in his commentary on Psalm 26. He notes that the practice of anointing in the Old Testament was normally reserved for either the king or the priest. But Christ now holds both offices as both Priest and King in virtue of his anointing or literally being the Messiah or Anointed one. Speaking of Christ, St. Augustine observes, "But not only was our Head anointed; but his body was too, we ourselves. . . . From this it is obvious that we are the body of Christ, being all anointed. In him all of us belong to Christ, but we are Christ too, because in some sense the whole Christ is Head and body" (Exposition 2 of Psalm 26). St. Augustine comments on John 3:13, "Nobody has gone up to heaven, except the one who came down from heaven." Our ability to be reborn and to go up to heaven occurs by the grace of God and through our communion with Christ who is the Head of his Body. The risen and ascended Christ is the font and origin of our sacramental participation in his grace. The Son of man is "one person in both natures" he is both "the Son of God equal to God" and "the Son of man taking to himself a human soul and human flesh" (Sermon 294). St. Augustine notes,
If you want to go up, be in the body of Christ. If you want to go up, be a member of Christ. For just as in one body we have many members, but all the members of the body, though they are many, are one body; so also is Christ (1 Corinthians 12:12); because Christ is head and body (Sermon 294).
St. Thomas Aquinas (1225-1274) highlights three aspects which are accomplished through Christ's bodily Ascension (Summa Theologiae 3a, q. 57-59). First, by his ascension Christ prepared a way for us to heaven. Second, the presence of Jesus' human nature in heaven allows him to intercede for us. Thirdly, Christ's enthronement in heaven as God and Lord, allows him to shower his divine gifts upon us (Eph. 4:10). The second reading for this Mass emphasizes this very point. "But grace was given to each of us according to the measure of Christ's gift." (Ephesians 4:7). Christ's bodily ascension allowed him to give the Church gifts of the Spirit "for building up the body of Christ" (Ephesians 4:12). The fullness of our participation in the Paschal mystery is made present in the Church through Christ's ascension and glorification in heaven. By our sacramental communion with Christ we become partakers in his divine life. Baptism (Romans 6:2-4); Confirmation (Ephesians 1:7-13) and Holy Eucharist (1 Corinthians 11:26) are all tied to the Paschal mystery. This is the central mystery of our faith which leads the eyes of our hearts be enlightened, in order that we might know what is "the hope that belongs to his call" (Ephesians 1:18). Holy Mary, Gate of Heaven, pray for us.