Returning to communion with God, after having lost it through sin, is a movement that springs from the grace of God, rich in mercy and desiring the salvation of men. It is necessary to ask for this precious gift for oneself and for others. (Catechism of the Catholic Church, 1439–1449).
Whoever wishes to receive Christ in Eucharistic Communion must be in a state of grace. If one is conscious of having committed mortal sin, one must not approach the Eucharist without first having received absolution in the sacrament of Penance. (Catechism of the Catholic Church, 1385, 1415).