This is a lesson about the Mass, the central act of worship. The lesson explains the Mass as a true sacrifice that recalls the sacrifice of Christ on the cross. It examines the prefigurations of the Mass in the Old Testament, particularly the Passover, and emphasizes the role of the priest as a minister of Christ in offering the sacrifice. The lesson also outlines the structure of the Mass, highlighting the Liturgy of the Word and the Liturgy of the Eucharist.