Pentecost Sunday is often called the birthday of the church. For the 
ancient Israelites, Pentecost (meaning ‘fiftieth’) was a harvest festival celebrated 50 days after the harvesting of the first sheaf. When theJerusalem temple was built, this harvest festival was transformed into a pilgrimage feast to celebrate the covenant that Israel had made with God on Mt Sinai. The Jews of the first century, including Christian Jews, celebrated the great pilgrimage feast of Pentecost. Several decades after the death of Jesus, the early Christians reflected on their origins and chose this feast to mark the birth of God’s new covenant with God’s people.
In today’s first reading (Acts 2:1-11), Luke tells the new Pentecost story in symbolic language that evokes the story of Moses and the people of Israel receiving God’s Law on Mt.Sinai. Just as God’s presence toIsrael was marked by earthquake and thunder and fire, so God’s Spirit enveloping the people of the new covenant appears in a mighty rush of wind and tongues of fire. Luke’s account also evokes early rabbinic teaching that the voice of God on Sinai divided into seventy tongues and all the nations received the Law in their own tongues.
For the content of the new covenant, we turn to the gospel reading from John 20:19-23. The risen Christ appears to the disciples who are huddled behind locked doors. He offers the simple greeting: “Peace be with you,” the greeting we offer each other at every Eucharistic celebration. He sends them on a mission of peace in continuity with his own God-inspired mission. He breathes on them the gift of the Holy Spirit and tells them that God will forgive those whom they forgive, and will ‘retain’ or ‘seize hold of’ the transgressions of those whose sins or transgressions they ‘retain’. To seize hold of evil-doing is to expose it and deal with it. Sometimes it is best to forgive and simply allow everyone to move on. In other situations, amnesty only exacerbates the problems. Much of the enduring conflict in our world derives from the inability of ordinary people and of leaders to know how to deal with transgression. The Holy Spirit is the unique source of our power to forgive, of our power to refrain from vengeance, and of our capacity to deal with or ‘retain’ the sins of the perpetrators of violence.