Final answer:
According to Stasiak, the most sacred and efficacious action of the church is the liturgy, which involves the performance of sacraments and serves as the church's primary form of worship and conveyance of grace.
Step-by-step explanation:
According to Stasiak, the action of the church that is most sacred and most efficacious is c. The liturgy. The liturgy refers to the set of rituals and ceremonies that are considered the formal act of worship in the Christian tradition. Within the Catholic Church, the sacraments, such as baptism and the Eucharist, play a central role in religious life and are administered by the church through its liturgical practices.
These sacraments are believed to be effective means of conveying God's grace to believers, thus making the liturgy a foundational aspect of Catholic worship and spiritual life. Additionally, the liturgy as a public form of worship encompasses the communal and performative dimensions that have been historically significant in uniting believers and preserving religious traditions.