In this sacramental dispensation of Christ's mystery the Holy Spirit acts in the same way as at other times in the economy of salvation: he prepares the Church to encounter her Lord; he recalls and makes Christ manifest to the faith of the assembly. By his transforming power, he makes the mystery of Christ present here and now. Finally the Spirit of communion unites the Church to the life and mission of Christ.
Source: Catechism of the Catholic Church (Vatican.va)