What does the Holy Spirit do in the Church?

What happened on Pentecost?

Fifty days after his Resurrection, the Lord sent the Holy Spirit down from heaven upon his disciples. The age of the Church began.

On Pentecost the Holy Spirit transformed fearful apostles into courageous witnesses to Christ. In a very short time, thousands had themselves baptized: it was the birthday of the Church. The miracle of the languages on Pentecost shows that the Church is there for all peoples from the very beginning: She is universal (= the Latin term for the Greek kat' holon, catholic) and missionary. She speaks to all men, overcomes ethnic and linguistic barriers, and can be understood by all. To this day the Holy Spirit is the "soul" of the Church, the essential principle of her life.

What does the Holy Spirit do in the Church?

The Holy Spirit builds up the Church and impels her. He reminds her of her mission. He calls people into her service and sends them the necessary gifts. He leads us ever deeper into communion with the Triune God.

Even though the Church during her long history has often seemed "abandoned by all good spirits", the Holy Spirit has been at work in her despite all the human failings and inadequacies. The mere fact of her two-thousand-year existence and the many saints of all eras and cultures are the visible proof of his presence. The Holy Spirit is the one who maintains the Church as a whole in the truth and leads her ever deeper into the knowledge of God. It is the Holy Spirit who works in the sacraments and brings Sacred Scripture to life for us. Even today he gives his gifts of grace (charisms) to those who are completely receptive to him. (YOUCAT questions 118-119)

Dig Deeper: CCC section (731-747) and other references here.