I have read, and believe it to be true, but am open to correction, that after one receives the sacraments of matrimony or confirmation while in a state of mortal sin, once the person goes to confession and is forgiven the sin, the graces of the other sacraments are then given to him. Is the same true for the Eucharist. Suppose that one goes to mass and for a stupid reason receives communion (while in a state of mortal sin), immediately after mass, he goes to confession and confesses both sins (the first mortal sin, and receiving communion unworthily). At that point, to the graces and effects of the Eucharist he received take effect? If not, why is this different than the other sacraments?
Penance gives sanctifying grace even for those not in a state of grace, and both Penance and Eucharist give and
increase of sanctifying grace for those already in a state of grace. Also, actual grace is given by these and a distinctive sacramental grace, corresponding to their respective purpose.
So the distinctive sacramental grace of the Eucharist was not received.The effect of this sacrament, which is produced in the soul of one who receives it worthily, is the union of him or her with Christ. Since by grace a person is incorporated in Christ and is united with his members, the consequence is that grace is increased by this sacrament in those who receive it worthily, and that every effect that material food and drink produce for corporal life — sustaining, increasing, repairing and delighting — this sacrament works for spiritual life. For in it, as Pope Urban said, we recall the gracious memory of our Saviour, we are withdrawn from evil, we are strengthened in good and we receive an increase of virtues and graces. Council of Florence, Session 3, Feb 15, 1438Once reborn and strengthened, we are nourished by the food of the divine eucharist. But if through sin we incur an illness of the soul, we are cured spiritually by penance.
Council of Florence, Session 8, Nov 22, 1439
In Penance the sinner is healed and re-established in ecclesial communion. In the Eucharist the sinner is healed of any venial sins, but never lost ecclesial communion.