The word Pentecost simply means “fiftieth day.” It was that day that the Holy Spirit was bestowed on the people of God. I think it’s important to understand that the Holy Spirit did not come into existence on the Day of Pentecost. Like the Father and the Son, the Holy Spirit has eternally pre-existed. Genesis 1:2 tells us that during the creation the Holy Spirit was hovering over the face of the deep. So the Spirit wasn’t invented at Pentecost. So what’s the difference? A simple way to think about it is that in the Old Testament the Holy Spirit worked with the people of God, energizing them to do God’s will. People like David and Samson experienced the Spirit this way. But from the Day of Pentecost on the Spirit began to dwell in the people of God. From “with” to “in.” See the difference?
So Pentecost means that the Spirit of God baptized believers into the body of Christ, and to dwell in every believer. John 14.16-17, “And I will pray the Father, and He will give you another Helper, that He may abide with you forever — the Spirit of truth, whom the world cannot receive, because it neither sees Him nor knows Him; but you know Him, for He dwells with you and will be in you.” Do you see the difference? Before Pentecost, He dwelt with His people; after Pentecost He dwells in His people.
What is the meaning of Pentecost? Pentecost simply means that now every born again believer, at the moment of salvation, is baptized by the Spirit into the body of Christ and is indwelled by the Spirit. The Spirit energizes and empowers the people of God to fulfill God’s mission for the world (Acts 1:8).