St. Thomas Aquinas gave an excellent Pentecost homily. Click here.
Here is a less worthy attempt… (But shorter at least!)
Come, Holy Spirit! On our dryness pour your dew.
We live by holding fast to the doctrines of our Catholic faith. At the same time, we also see visible signs of the mysteries we believe in. Let us try to understand how the mystery of Pentecost fits into the annual rites of spring.
First, the basic facts: The Lord Jesus died on the cross. On the third day, He rose again. He remained on earth for forty days. Then He ascended into heaven. The Apostles prayed. Then Christ poured out the Holy Spirit.