The Holy Spirit is the creator of the Church.
People often wonder what was unique about Jesus of Nazareth. After all, He taught people to do unto others as they would have done unto them, a universal truth taught by virtually every major world religion, in one form or another. (A prime bit of evidence that the Bible's assertion that God, His nature, and His will are known by all.)
And in teaching that God's greatest command is that we love God and love neighbor, Jesus was merely underscoring the teachings of the Old Testament going back to the two tables of the Ten Commandments.
Except for one teaching, what made Jesus unique was not what He said, but what He did. In dying as the perfect, sinless representative of the human race, He accepted our rightful punishment for sin and in rising, He opened up eternity to all who believe in Him. Though Jesus was the greatest teacher in the history of the world, Christians don't have faith in His teaching. We have faith in Him.
But what was that one unique idea that Jesus taught? It comes in John's Gospel where Jesus says, "I give you a new commandment, that you love one another. Just as I have loved you, you also should love one another. By this everyone will know that you are my disciples, if you have love for one another.” (John 13:34-35)
How is that unique? Isn't it just a reiteration of the Great Commandment? No. Here, Jesus is saying that by way of His death and resurrection, a new community is going to be created, a community composed of Jews and non-Jews (Gentiles) who share a common belief in Him as God and Savior and share a common mission to share His love with the world. The love shared by this community of faith is to be the primary witness to the world about the life-transforming Good News of Jesus. This community is the Church.
Christians are blessed to be members of this community and by expressing Christ's love in words and deeds, they invite others to be part of it.
An old story says that a man was convicted of a crime for which the punishment was death, though it was never clear to people if the man was actually guilty. A friend of the man fell before the king's feet, begging that his own life be taken instead of that of his friend. "My friend has a wife and children who need him," the friend implored. "But I am widower without children. Please kill me and not my friend, sir!" Overwhelmed by the love this man bore for his friend, the king pardoned the first man, released the second, and then asked, "May I ask a favor of you two? May I be your friend as well? I would feel privileged to be part of such a community of love!"
The Bible records that the early Christians so loved one another that others, like that king, wanted to be part of their community of love. "See how they love one another," they said in amazement.
On Pentecost Day, fifty days after Jesus' resurrection and ten days after He ascended to heaven, the Holy Spirit gave birth to the Church, a community of love and a family of believers that will live for all eternity. It's in such a community of love and family of believers that my former atheism withered and died and new life in Christ took root in me!