Of all seven sacraments, the Holy Eucharist, or Holy Communion, is the most central and important to Catholicism. Holy Communion is offered at every Mass, and in fact, the ritual of the Mass is largely taken up with preparing the hosts (wafers made of wheat and water, or gluten-free) and wine to become the body and blood of Christ and the congregation to receive the body of Christ. Transubstantiation is the act of changing the substances of bread and wine into the substances of the Body and Blood of Christ.