At Pentecost, the Holy Spirit comes down upon the Apostles, giving them the power to speak in tongues for the proclamation of the Gospel to the nations. In the midst of that narrative, however, we have St. Peter preaching about how the events unfolding were a fulfillment of Old Testament prophecy. He begins by reciting from Joel 3:1-5 (or 2:28-32 in other versions), which predicts that God will pour out His Spirit upon all flesh (and is also one of the readings recited during the Vigil Mass).
The term “all flesh” is significant because it foretells the global scope of the outpouring of God’s Spirit. The religion of the Old Testament is seen as nationalistic and centred almost entirely on the welfare and destiny of the Jewish nation. In the midst of that emphasis, however, we see statements such as these which hint that God’s ultimate plan isn’t just for the welfare of one nation, but for all. We see this as well in other places, such as in Isaiah 42, which speaks about how when the Messiah comes, he will bring justice to all the nations (verse 1), and that He will be a light to those nations (verse 6).
The timing of this outpouring is highly significant as well. Today the Jewish calendar marks the festival of Shavuot (Heb. שָׁבוּעוֹת, lit. “weeks”), which is observed fifty days after the beginning of the Counting of the Omer, which is recorded in Leviticus 23, and from which we derive the Greek term Pentecost (Gk. Πεντηκοστή, lit. “fiftieth”). This festival commemorates the giving of the Torah to Moses, as well as the bringing in of the wheat harvest to the temple in Jerusalem.
This motif of bringing in the harvest becomes significant once we get to the New Testament. Jesus often used harvesting in His parables as a metaphor for the conversion of the nations. On the Shavuot of AD 33, a different kind of harvest began to be brought into God’s temple–a harvest of souls, rather than wheat. This harvest continues 2,000 years later, as members of every nation, tribe and tongue are brought from the fields of the world into the temple of Christ’s Church.