Come, Sweet Paraclete!
Imagine if you will the Apostles in the upper room.  Jesus has just ascended into Heaven and they are sitting around, twiddling their thumbs, wondering, “What the camel are we gonna do now?”  Maybe one of them looks over at Peter, who responds with something to the effect of, “I’m just as lost as you are, guys.”
Meanwhile let’s imagine that Jesus is back up in Heaven, looking down at His disheartened Apostles, His beloved friends.  He turns to the Father and says, “Is it time to send him down there?”  “Yes, My Son, it is time.”
Back on Earth in the upper room, a sudden mighty wind shakes the walls, causing the Apostles to look around frantically and jump from their chairs.  Darting their eyes upward, they see a large flame above them.  The single flame splits into individual flames, each one resting atop their heads.   A deep sense of peace and power fill them from within, casting out all the fear and uncertainty that had been perturbing them.  As if their bodies are functioning without them, they begin speaking in other languages as if they have been fluent their whole lives.
That night in the upper room, the Holy Spirit made his public debut as he came upon the Apostles and overshadowed them with the love of God.

Friend and Champion
So before I explain Pentecost, I think it would help to understand the Holy Spirit himself.  Who is he, a distant force or a most determined Advocate of our salvation?
The Holy Spirit is the third person of the Trinity.  He is the love between the Father and the Son manifested.  While the dove from above does make his official appearance in the Acts of the Apostles, we are foretold of him through the Old Testament, starting with Genesis.

Genesis 1:1-2, “In the beginning when God created the heavens and the earth, the earth was a formless void and darkness covered the face of the deep, while a mighty wind swept over the face of the waters.”

Did you catch that last line?  “…while a mighty wind swept over the face of the waters?”  Sound familiar?  The Spirit came in the form of a mighty wind that shook the walls of the upper room where the Apostles were residing.

We see him again in the Book of Samuel just after Samuel anointed Saul.

1 Samuel 10:10, “When they came to the hill, there was a group of prophets to meet him; then the Spirit of God came upon him, and he prophesied among them.”

It is not until the Annunciation when we finally hear of the Holy Spirit by name.  After she is told that she will give birth to the Messiah, Mary reasonably asks the Archangel Gabriel how this virgin birth is to happen, “since I have no relations with a man?” she questions.

Luke 1:35, “The Angel answered, “The Holy Spirit will come upon you, and the power of the Most High will overshadow you.”

Then, at Jesus’ baptism, there is a visual representation of the Holy Spirit.

Matthew 13:16-17, “After Jesus was baptized, he came up from the water and behold, the heavens were opened [for him], and he saw the Spirit of God descending like a dove [and] coming upon him.  And a voice came from the heavens, saying, “This is my beloved Son, with whom I AM well pleased.”

We can safely say that the Holy Spirit has been active throughout history and continues to be flying around the globe to this day.  With this logic, we can conclude that the Holy Spirit is not some vague, distant ghost who does little and says even less.  The third person of the Trinity is alive, vibrant and ever seeking the salvation of our souls.  There’s a reason why he is also known as the Advocate, Comforter, Helper and so on.  Sometimes the Holy Spirit comes upon us as a roar, a mighty wind that shakes us to our core and wakes us from our apathy.  Other times the Holy Spirit is like a feather landing on our heads; sudden but gentle.  He whispers to us and caresses our souls with the love of the Father.
Now that we know who the Holy Spirit is, we can move on to understanding what Pentecost is.

A Church is Born
Pentecost is what happened in that upper room.  The Holy Spirit, having first appeared to Mary in a private setting, then revealing himself again in the public setting of Jesus’ baptism, was now making himself known once more in a small room where the apostles were gathered in seclusion.  He came upon them and brought them out of their isolation, bursting open the closed doors of fear and doubt into a world hungry for the Good News.  He empowered them, equipped them and readied them for their mission: To preach the Gospel to every living creature and baptize the masses in the Name of the Father, and of the Son and of the Holy Spirit.
This mission is alive and well today.  It is the duty of every Christian to pick up the torch that was handed down to us at our baptism.  However, our world does not make that task easy at all.  Our world fights against us, making that path difficult to say the least.  This is where the help of the Holy Spirit is absolutely needed.  As scripture has shown us, the Holy Spirit is not an abstraction or an uninvolved force; he is a person.   He is the love between the Father and the Son and as it says in 1 John 4:18, “Perfect love casts out fear.”  As our advocate, he speaks to us and for us.  As our comforter, he lifts us up when we are knocked down.  As our helper, he guides us to wisdom and truth.  As our friend, he is always there for us and ready to stand beside us.

Let us end this piece with a prayer to the Holy Spirit.

Holy Spirit, you are welcome here.
In your presence there is no room for fear or anxiety.
You are the champion of our souls and the fiery advocate for our salvation.
Come fill our minds with knowledge and truth.
Come fill our hearts with compassion and love of neighbor.
Come fill our souls with the peace of Christ that surpasses all understanding.
May your friendship and unfailing help in our lives shape us into the men and women Christ has called us to be.

Amen.