Holy in ancient languages all refer to this special quality of God

Greek - hagios

Hebrew - gadosh

Latin - sanctus

The holiness of the Church arises from the mystery of Christ's love. By the grace of Baptism, through the Holy Eucharist, Sacrament of Penance and Reconciliation, and all the Sacraments, Catholics become holy with God.

The Church is holy because Christ shares his own life with the Church. The Church remains holy because the Holy Spirit dwells in her.