The Eucharist, also called the Blessed Sacrament, is the sacrament (the third of Christian initiation, the one that the Catechism of the Catholic Church says “completes Christian initiation”) by which Catholics partake of the Body and Blood of Jesus Christ and participate in his one sacrifice. The first of these two aspects of the sacrament is also called Holy Communion. The bread (which must be wheaten, and which is unleavened in the Latin, Armenian and Ethiopic Rites, but is leavened in most Eastern Rites) and wine (which must be from grapes) used in the Eucharistic rite are, in Catholic faith, transformed in its inner reality, though not in appearance, into the Body and Blood of Christ, a change that is called transubstantiation. “The minister who is able to confect the sacrament of the Eucharist in the person of Christ is a validly ordained priest alone.” The word “priest” here (in Latin sacerdos) includes both bishops and those priests who are also called presbyters. Deacons as well as priests (sacerdotes) are ordinary ministers of Holy Communion, and lay people may be authorized in limited circumstances to act as extraordinary ministers of Holy Communion. The Eucharist is seen as “the source and summit” of Christian living, the high point of God’s sanctifying action on the faithful and of their worship of God, the point of contact between them and the liturgy of heaven. So important is it that participation in the Eucharistic celebration (see Mass) is seen as obligatory on every Sunday and holy day of obligation and is recommended on other days. Also recommended for those who participate in the Mass is reception, with the proper dispositions, of Holy Communion. This is seen as obligatory at least once a year, during Eastertide.