Each of us is a Temple of the Holy Spirit because we are anointed by the Spirit through the Sacraments of Baptism (Catechism of the Catholic Church (CCC), 2000, para. 1226) and Confirmation (CCC, 2000, para. 1287-1289). In addition, we receive the Spiritual Gifts from the Spirit.
The drawing to the right shows the artist depiction of the scene in Acts of the Apostles. It shows the awesome power of the Holy Spirit given as a gift from God to the Apostles.
That gift changes us, just like it changed the Apostles, because the Holy Spirit—the Third Person of the Holy Trinity—now lives within us. Please take some time to let that thought sink in. If you ever thought that God was in Heaven looking down on us from afar, it is quite a revelation when you to realize the Holy Spirit actually lives in each of us who were baptized with water “in the name of the Father, and of the Son, and of the Holy Spirit.”