With what measure you measure, it shall be measured to you, and more shall be given to you.
When my friend Mike attends a baseball game, he will, depending on where he is seated, bring a mitt with him. He wants to be ready to catch a line drive. Good thinking! Fans who show up at games without gloves will be ill-prepared to catch the balls that come their way. In fact, attempting to catch a speeding ball with an ungloved hand may prove injurious.
I think something similar can be said about receiving Holy Communion. We ought to partake of the Eucharist, not with baseball gloves, but with hearts protected by grace, in other words, with souls free from the stain of mortal sin. That way we will be sure to catch the additional graces the Lord sends us through the Sacrament. If we are conscious of having committed a mortal sin, we must go to confession prior to receiving Holy Communion. To do otherwise would be utter foolishness. As a matter of fact, attempting to receive the Eucharist with mortal sin on our souls is like trying to catch a line drive without a baseball mitt. It may be very injurious. It may result in an even greater sin!