He would be guilty of mortal sin, because he exposes himself to the danger of grievously offending God. Hence, before he acts he must lay aside the doubt; and if he has not hitherto done so, he must confess it, at least, as it is before God. But the scrupulous, who have doubts about everything, must follow another rule: they must obey their confessor. When he tells them to conquer their doubts, and to act against scruples, they should obey with exactness; otherwise they will render themselves unable and unfit to perform any spiritual exercise.
Alphonsus LiguoriCertainly amongst all devotions, after that of receiving the sacraments, that of adoring Jesus in the Blessed Sacrament holds first place, is most pleasing to God, and most useful to ourselves. Do not then, O devout soul, refuse to begin this devotion; and forsaking the conversation of men, dwell each day, from this time forward, for at least half or quarter of an hour, in some church, in the presence of Jesus Christ under the sacramental species. Taste and see how sweet is the Lord.
Alphonsus LiguoriLove tends to union with the object loved. Now Jesus Christ loves a soul that is in a state of grace with immense love; He ardently desires to unite Himself with it. That is what Holy Communion does
Alphonsus Liguori