"The Eucharist is the heart and the summit of the Church's life, for in it Christ associates his Church and all her members with his sacrifice of praise and thanksgiving offered once for all on the cross to his Father; by this sacrifice he pours ou the graces of salvation on his Body which is the Church."
(Catechism of the Catholic Church ¶ 1407)
"Anyone who desires to receive Christ in Eucharistic communion must be in the state of grace. Anyone aware of having sinned mortally must not receive communion without having recieved absolution in the sacrament of penance."
"The Church warmly recommends that the faithful recieve Holy Communion when they particitpate in the celebration of the Eucharist; she obliges them to do so at least one a year."
(Catechism of the Catholic Church ¶1415, ¶1417)