What is the meaning of the Coming of the Holy Ghost? What did it accomplish? How did He tell us of His Presence; reveal It to us? By the fact that all spoke in the tongues of every nation. There were a hundred and twenty people gathered in one room; ten times twelve. The sacred number of the Apostles was multiplied ten times. What then, did each one upon whom the Holy Spirit descended speak in one of the tongues of each of the nations: to this man one language, to this man another, dividing as it were among themselves the tongues of all the nations? No, it was not so: but each man, singly, spoke in the tongue of every nation. One and the same man spoke the tongue of every nation: the unity of the Church amid the tongues of all the nations. See here how the unity of the Catholic Church spread throughout all nations is set before us.
The Holy Spirit not outside the Church.
He therefore who possesses the Holy Spirit is in the Church, which speaks in the tongues of all nations. Whosoever is without this Church, has not the Holy Spirit. For this reason the Holy Spirit deigned to reveal Himself in the tongues of all nations, that each may understand, that he possesses the Holy Spirit who is nourished within the unity of the Church, which speaks in every tongue. One body, says Paul the Apostle, one body and one Spirit (Eph. iv. 4).
Attend to this, you who are our members. A body is composed of many members, and one spirit gives life to all the members. By the human spirit, by which I am myself a man, I join together all my members: I command my members to move, I direct the eye to see, the ears to hear, the tongue to speak, the hand to work, the feet to walk. The duties of each member are different, but one soul joins all together. Many things are commanded, many done, but one commands, one is obeyed. What our spirit, that is, our soul, is to our own members, this the Holy Spirit is to the members of Christ, to the Body of Christ, which is the Church.– St. Augustine