COMMUNION/ EUCHARIST
"At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood. This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet 'in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us.'" (CCC 1323, see also Luke 22:19, John 6:53, 1 Corinthians 11: 23-30,  Acts 2:42, Bible/Early Church References link)

Receiving Communion
Adult Catholics wishing to receive the Holy Eucharist in daily Mass must not be in grave (mortal) sin when receiving this sacrament; else they must have recourse to the Sacrament of Reconciliation.