Jesus' baptism marks the beginning of His public ministry. John the Baptist is holding a shell, a traditional symbol of baptism, from which three drops of water are falling on Jesus, representing the Holy Trinity. The top medallion features both a bright light and a dove. The light is a reminder that the Father spoke from heaven: "This is My beloved Son, with whom I am well pleased," and the Holy Spirit descended upon Jesus as a dove.
John the Baptist is holding a staff that forms a cross. At His baptism, Jesus began His ministry that would culminate in the cross. The cross also reminds us that through Baptism we are joined to Christ's death and resurrection (Romans 6:1-11).
The medallions at the top of the window represent Jesus as the Lamb of God. It was John the Baptist who confessed that Jesus was "the Lamb of God who takes the sin of the world." The Lamb on the left is the suffering lamb as the lamb is pierced and the blood is flowing into a chalice. Jesus was the prefect Lamb who was sacrificed on the cross for our sins. The right medallion is of the triumphant lamb. Because of His death and resurrection, Jesus is the victorious Lamb now seated on the throne who is worthy to receive all glory and honor, thanks and praise.