Pentecost is a Greek word which means fiftieth. This fiftieth day, celebrated by the Jewish people, is counted from the day on which the paschal lamb was sacrificed; and that is done, because fifty days after the exodus from Egypt, the Law was given on the blazing summit of Mount Sinai. Similarly, in the New Testament, the Holy Spirit came down on the apostles fifty days after Christs Passover and appeared to them in the form of fire. The Law was given on Mount Sinai, the Spirit on Mount Zion; the Law on top of the mountain, the Spirit in the Cenacle.
All the disciples were gathered in one place. Suddenly, there came a great noise. As a Psalm says, There is a stream whose runlets gladden the city of God (Ps 46:5). A great noise accompanied the coming of the one who came to teach the faithful. Note how this agrees with what we read in Exodus: On the morning of the third day there were peals of thunder and lightning, and a heavy cloud over the mountain, and a very loud trumpet blast, so that all the people in the camp trembled (19:16). The first day was the incarnation of Christ; the second day was his passion; the third day, the Holy Spirit was sent. This day came: thunder is heard, there was a great noise; lightning flashed the apostles miracles; a thick cloud compunction of heart and repentance covered the mountain, the people of Jerusalem (Acts 2:37-38).
Tongues as of fire appeared. Tongues those of the serpent, of Eve and Adam, had given death access to this world. That is why the Spirit appeared in the form of tongues, opposing tongues with tongues, healing the fatal poison by means of fire. They began to speak. That is the sign of fullness; the full vessel overflows; the fire cannot contain itself. These diverse tongues are the various lessons that Christ left us, such as humility, poverty, patience, obedience. We speak in these various tongues when we give our neighbor an example of these virtues. The word is alive when the works speak. Let us make our works speak!
-Saint Anthony of Padua