A blessed Pentecost!
Much can be said of the Holy Spirit on Pentecost but I will limit myself to a few items.
The Holy Spirit is understood and taught by the Magisterium of the Catholic Church as being:
1. “the soul of the Church”;
2. “the principle of being and life in the Church… [as Divine Being who] welds together the members of the Church among themselves and with Christ the head”;
3. as “Where the Church is, there is also the Spirit of God; and where the Spirit of God is, there is the Church and all grace” (St Ignatius of Antioch);
4. “the heart of the Church (for Ecclesiae)” (Aquinas);
5. [the Spirit is the principle] that principle … that unites, quickens, teaches, sanctifies the Church, indwells in her, communicates the riches of the one to the others” (Aquinas).
Come Holy Spirit, come through Mary.